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J M Tyler

Publications and source records attributed to J M Tyler.

At least 19 recordsLinked to original sources
PubMed1990

Medium flow rate modulates autocrine-paracrine feedback of GH and PRL release by perifused GH3 cells.

We previously documented both the spontaneous acceleration of growth hormone (GH) and prolactin (PRL) production by GH3 cells during perifusion and the suppression of their production during plate culture. We here present the role played by medium flow itself in this differential behavior. Increasing rates of perifusion flow (pump rates of 1 to 5 ml/h, equivalent to chamber flow rates of 0.19 to 1.3 microliters.min-1.mm-2 of cross-sectional area) were associated with enhanced GH and PRL secretion. Flow rate-dependent basal hormone secretion rates were established quickly and were stable for the first 10 to 14 h of perifusion. The previously documented independent, spontaneous, and continuously accelerating production of both hormones that followed during the subsequent 40 (PRL) to 60 (GH) h of perifusion was also shown to be flow-rate related. Any time the rate of medium flow was changed within an experiment, the rate of hormone secretion was modulated. However, that modulation did not interrupt ongoing flow-associated acceleration of hormone production once the latter had begun. In addition, GH3 cell product(s) from one cell column reversibly inhibited secretion from cells in a downstream column. The inhibition did not occur when cells in the downstream column had been exposed to trypsin. Other work had suggested that neither GH, PRL, insulinlike growth factor-I, leucine, nor nutrient exhaustion were responsible for the effect. These data are consistent with autocrine-paracrine feedback regulation of GH3 cells by a secretory product(s). Feedback would thus provide a mechanism to effect flow-rate-dependent modulation of GH and PRL release, and to explain accelerating hormone production during perifusion.

Animals↗
PubMed1990

Contribution of stored rat growth hormone to restoration of depleted rat pituitary immediate release pools.

UNLABELLED: Stored rat pituitary growth hormone (GH) is functionally divided into immediately releasable and more stable compartments. These observations are consistent with either intracellular hormone compartmentalization within cells of a functionally homogeneous somatotroph population or summed responses from a heterogeneous population of functionally specialized cell subgroups. We investigated the pituitary's ability to recruit stored rGH to replenish depleted immediate release pools. We used perifused pituitary fragments whose stored rGH was labeled during pre-incubation in the presence of [3H]leucine. Initial immediate release pool depletion was accomplished by continuous exposure to combined 21 mM potassium ion (K+) and 1 mM dibutyryl cyclic AMP (dbcAMP). During a subsequent perifusion period in the presence of either no secretagogue, continuing 21 mM K+, or continuing 1 mM dbcAMP, we examined release of stored [3H]rGH in response to repetitive 15 min pulses of 21 mM K+ or 1 mM dbcAMP. Analysis was by specific immunoprecipitation. We had demonstrated that K+ and dbcAMP pulses can stimulate repetitive, albeit diminishing, stored [3H]rGH release responses. However, following pre-treatment with combined 21 mM K+ and 1 mM dbcAMP: (i) pulses of dbcAMP stimulated almost no stored [3H]rGH release in the presence of 21 mM K+ or in the absence of a background secretagogue; and (ii) stored [3H]rGH release in response to pulses of K+ was attenuated in the absence of background secretagogue but fully restored in the presence of dbcAMP. CONCLUSIONS: (i) at least some individual somatotrophs can compartmentalize stored hormone; and (ii) an active transport system facilitates restoration of somatotroph immediate release pools using stored rGH.

Animals↗
PubMed1989

Autocrine-paracrine inhibition of growth hormone and prolactin production by GH3 cell-conditioned medium.

In previous work we have shown that perifused GH3 cells exhibit spontaneously accelerating growth hormone (GH) and prolactin (PRL) secretory rates. This behavior contrasts with GH and PRL secretion rates that are decreasing or stable over the same 3-d period in static cell culture. We now report that GH3 cells maintained in serum-supplemented medium produce an autocrine-paracrine factor(s) which inhibits GH secretion in plate culture; PRL release is frequently reduced as well. The inhibitory effect of conditioned medium on GH secretion was concentration dependent, whereas PRL release was stimulated at low and inhibited at high concentrations over the same range. Extensive dialysis of conditioned medium using membranes with a molecular weight cut-off of 12,000-14,000 did not remove GH inhibition but produced a retentate that stimulated PRL secretion. Heat-inactivation of conditioned medium did not abolish inhibition of GH release but did remove the PRL-stimulatory effect. IGF-I added to fresh culture medium did not reproduce the GH-inhibitory effects of conditioned medium. We conclude that GH3 cell secretory behavior in perifusion and plate culture systems may be partially explained by the production of an autocrine-paracrine factor: its accumulation in plate culture inhibits GH and PRL secretion whereas its removal, by perifusing medium, allows GH and PRL secretion to accelerate.

Animals↗
PubMed1989

Monensin influences basal and human growth hormone-releasing hormone 44-induced release of stored and new rat growth hormone and prolactin.

When previous data suggested a growth hormone-releasing factor (GRF)-sensitive branch in intracellular hormone processing, the monensin-sensitive Golgi apparatus seemed a likely candidate. We examined monensin's effect on basal and GRF-stimulated release of newly synthesized and stored rat growth hormone (rGH) and rat prolactin (rPRL). 14C-Pre-labeled, perifused rat pituitary fragments were exposed to [3H]leucine in 0-10 microM monensin; a pulse of 3 nM GRF assessed subsequent secretory responsivity. Monensin dose-dependently reduced basal release of stored [14C]rGH and [14C]rPRL. GRF-stimulated release of stored [14C]hormone was doubled after 0.03 microM and 0.1 microM monensin; higher concentrations diminished stored hormone release. Low concentrations of monensin accelerated basal (0.03 microM and 0.1 microM) and GRF-stimulated (0.03 microM) [3H]rGH and [3H]rPRL release without altering recovery; higher monensin concentrations (greater than or equal to 1 microM) reduced basal, and abolished GRF-stimulated, new hormone release and reduced total [3H]rGH and [3H]rPRL recovery. These data are consistent with a GRF-sensitive and monensin-influenced branch in intracellular hormone processing that regulates the fraction of new hormone exiting the cell without prior immersion in storage compartments.

Animals↗
PubMed1989

Pituitary immediate release pools of growth hormone and prolactin are preferentially refilled by new rather than stored hormone.

Pituitary stores of rat GH (rGH) and PRL (rPRL) are divisible into immediately releasable and more stable compartments representing either compartmentalized hormone within individual cells of a homogeneous population or responses of specialized cell subsets in a functionally heterogeneous population. In addition, newly synthesized rGH and rPRL can be processed either into intracellular storage or toward direct release. Fractional assignment of new hormone to these two paths can be influenced in the somatotroph by GHRH and may also represent either intracellular processes or functional heterogeneity of cells. We investigated the source, newly synthesized or stored, of hormone refilling the somatotroph and lactotroph immediately releasable pools (IRP) after their discharge by 21 mM potassium ion, 1 mM (Bu)2cAMP, 3 nM human GHRH-44, or 3 microM prostaglandin E1. Experiments were performed using perifused pituitary fragments exposed sequentially to [14C]- and [3H]leucine in association with stimulation by two 30-min pulses of the same secretagogue. Therefore, only [14C]hormone was available for release by the first stimulus, whereas both [14C]- and [3H]hormone were available for release by the second stimulus. Analysis was by specific immunoprecipitation. The first episode of stored [14C]rGH release exceeded the second episode of stored [14C]rGH release in response to each secretagogue. However, release of newly synthesized [3H]rGH in response to the second episode of stimulation exceeded the simultaneous release of stored [14C]rGH while matching or exceeding the [14C]rGH release that had occurred in the same experiment in response to the first episode of stimulation. Refilling both GH and PRL IRP stores drew primarily upon newly synthesized hormone, but with different secretagogue-specific patterns. These data confirm differential handling of new and stored rGH and rPRL within the pituitary. They are consistent with either (1) the enhanced shunting of newly synthesized hormone to IRPs within cells that are capable of compartmentalized intracellular hormone storage, or (2) the relatively complete discharge of a subset of somatotrophs and lactotrophs that are specialized to deliver pulsed hormone release, after which they are refilled by newly synthesized hormone.

Alprostadil↗
PubMed1988

Fractional reduction of somatostatin concentration interacted with rat growth hormone releasing hormone to titrate the magnitude of pulsatile growth hormone and prolactin release in perifusion.

Growth hormone (GH) pulses in vivo are associated with increased hypothalamic portal growth hormone releasing hormone (GH-RH) concentration and can be prevented by GH-RH antisera. GH pulses are also associated with prior reduction of portal somatostatin (SRIF) concentrations, although SRIF antisera do not abolish GH pulses. In vitro, pulses of GH-RH as well as SRIF withdrawal are followed by pulses of GH release; the presence of GH-RH enhances post-SRIF GH release. We asked four questions: (1) During combined GHRH-SRIF exposure in vitro, must SRIF withdrawal be complete to produce a pulse of GH release, or is there a threshold diminution of SRIF which permits it? (2) When pulsatile GH release does occur, is it an all-or-none phenomenon, or is it titratable by fractional reduction of SRIF? (3) Does varying the GH-RH concentration while administering SRIF systematically alter GH release in response to fractional SRIF reduction? (4) Given a small but distinct effect of GH-RH on release of stored prolactin (PRL) in this system, does fractional SRIF reduction alter PRL release in parallel? Rat pituitary tissue whose hormone stores had been prelabeled with tritium was perifused for 120 min in combined 25 nM SRIF and 3 or 10 nM rat GH-RH (rGH-RH). Then, while maintaining rGH-RH concentrations, the SRIF concentration was left unchanged (control) or was reduced to 20, 15, 10, 5, or 0 nM for 60 min. Release of stored rGH and rPRL was assessed by immunoprecipitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Combined effects of human growth hormone (GH)-releasing factor-44 (GRF) and somatostatin (SRIF) on post-SRIF rebound release of GH and prolactin: a model for GRF-SRIF modulation of secretion.

Somatostatin (SRIF) and GRFs play key roles in regulating GH secretion. We previously presented a model of SRIF-cAMP interaction; SRIF blocks rat (r) GH release without preventing its accumulation in a potentially releasable pool. This phenomenon may represent a mechanism whereby tonic SRIF inhibition and its subsequent reduction or withdrawal can modulate the magnitude if not the initiation of rGH pulses. Herein we test that model using human GRF-44 (hGRF-44). Tritium-prelabeled rat anterior pituitary fragments were perifused until stored [3H]rGH and [3H]rPRL release rates were stable. SRIF (10 or 25 nM), with and without hGRF-44 (3 or 10 nM), was added in short (1-h hGRF-44) and long (3-h hGRF-44) protocols; SRIF was then withdrawn while hGRF-44 was continued. Release of stored prelabeled [3H]rGH and [3H]rPRL was assessed by immunoprecipitation. Effects on PRL release were followed for comparison. SRIF-induced inhibition of release was only partially reversed by hGRF-44. At these concentrations and so long as SRIF was present, hGRF-44 could not stimulate the rate of hormone release to values above pre-SRIF basal rates. On the other hand, the amplitude of post-SRIF rebound release was increased by prolonging exposure to SRIF alone, by including hGRF-44 with SRIF, by increasing the amount of hGRF-44 included with SRIF, by prolonging exposure to hGRF-44 plus SRIF, and by using a smaller concentration of SRIF during exposure to hGRF-44. Interaction of hGRF-44-SRIF effects generated peak rates of hormone release after SRIF withdrawal which exceeded the maximum rates achieved using hGRF-44 alone in this system. Lactotroph responses were much smaller, but qualitatively resembled somatotroph responses. We conclude that the interplay of simultaneous hGRF-44 and SRIF effects can regulate the amplitude of rGH pulses. Although GRF can initiate physiological GH release, and GRF antisera can block GH pulses, we suggest that the surge of release that follows reduction of SRIF-induced inhibitory tone in vitro represents a potential mechanism that could contribute to the initiation of some pulses of release. Finally, we also present a theoretical model of secretagogue interactions at the cellular level to explain our results. The model is compatible with either a homogeneous cell population in which each secretory cell has multiple capabilities or a heterogeneous cell population composed of cell subgroups with complementary secretory abilities.

Animals↗
PubMed1987

Deleterious effects of fungizone on growth hormone and prolactin secretion by cultured GH3 cells.

The rates at which growth hormone (GH) and prolactin (PRL) are spontaneously secreted from a rat pituitary tumor cell line (GH3) were significantly reduced when these cells were maintained in medium containing 2.5 micrograms/ml Fungizone (Fz). The reduction in hormone secretion was not immediately reversed by removal of Fz during perifusion, but after 3 wk in control medium, secretory rates approached the pre-Fz treatment levels. In plated cells, secretion of GH was reduced by Fz in a dose-dependent manner, whereas PRL secretion was significantly reduced only by the highest concentration (2.5 micrograms/ml) of Fz. We concluded that Fz is not an acceptable medium constituent for the long-term culture of GH3 cells. However, because its effects are reversible, its short-term use as a decontaminating agent might eliminate the necessity for reinitiating the culture of cells whose secretory behavior must be followed in long-term protocols.

Amphotericin B↗
PubMed1987

GH3 cell secretion of growth hormone and prolactin increases spontaneously during perifusion.

UNLABELLED: GH3 cell secretory activity was studied in long-term perifusion to define previously reported spontaneous increases in growth hormone (GH) and prolactin production (PRL). Mechanically harvested cells (1 X 10(7)/column) were perifused at 4 ml/h for 72 h. A basal period of variable duration (8 to 12 h), during which hormone secretion was stable, was followed by steadily increasing secretion rates. Changes in cell number were not sufficient to account for increased hormone secretion rates: a) there was no significant change in cell count after 72 h (0.97 +/- 0.03 X 10(7); n = 18); b) mean cell column DNA content increased 25.5% above the base value, whereas GH secretion rose 385% and PRL rose 178% (n = 5). Observed differences in the duration of the basal secretion period, the basal secretory rate, and the magnitude of secretory rate increase were associated with several variables: a) variability within a subline was a function of passage number: GH secretion decreased and PRL secretion increased with subculture number; b) cells with identical lot and freeze numbers, but received at different times, behaved differently; c) the presence of an antifungal agent (nystatin) altered hormone secretion reproducibly. CONCLUSIONS: a) rates of GH and PRL secretion rise spontaneously in perifusion without a proportional increase in GH3 cell number; b) fluctuations in the rate of GH3 cell secretion of GH and PRL are not entirely random but are determined by several definable variables.

Animals↗
PubMed1987

Growth hormone-releasing factor-44 specificity for components of somatotroph and lactotroph immediate release pool substructures.

Rat somatotroph and lactotroph hormone storage is divisible into at least two functional compartments: an immediate release pool (IRP) and a pool that responds to prolonged stimulation. An IRP substructure has been defined by release in response to potassium ion (K+), prostaglandin E1 (PGE1), and Bu2cAMP. The somatotroph IRP is expandable; the lactotroph IRP is fixed in size. The present experiments examined which IRP components contribute to the rapid release of stored GH in response to GH-releasing factor-44 (GRF). Release of stored PRL was monitored for comparison. In vitro prelabeling defined stored rat (r) GH and rPRL. Release in response to 21 mM K+, 3 microM PGE1, 1 mM Bu2cAMP, and/or 3 nM GRF was monitored with a perifusion-immunoprecipitation system. After 120 min of basal perifusion, tissue was exposed to one of the four secretagogues for 90 min. During a second 90-min period a second secretagogue was added while exposure to the first secretagogue continued. We demonstrated that 21 mM K+ reduces peak rGH release in response to 3 nM GRF by 52%, whereas GRF does not reduce rGH release in response to K+; 3 microM PGE1 reduces rGH release in response to GRF by only 19% although GRF reduces rGH release in response to PGE1 by 88%; 1 mM Bu2cAMP reduces rGH release in response to GRF by 87%, and GRF eliminates rGH release in response to Bu2cAMP (1.2% of control value); combined K+ plus Bu2cAMP reduce rGH release in response to GRF to 2.5% of the control value, whereas after GRF pretreatment rGH release in response to combined K+ plus Bu2cAMP is 93% of the control value; and combined PGE1 and Bu2cAMP reduce the response to GRF to 17% of the control value. Effects on rPRL release are qualitatively similar. We conclude that immediate GRF-stimulated release of stored rGH originates in the somatotroph IRP components defined by responses to PGE1 and Bu2cAMP; it derives only slightly, if at all, from the IRP component defined by the response to K+. The smaller GRF-stimulated release of IRP rPRL is similarly derived.

Alprostadil↗
PubMed1986

Release of stored, pre-labeled growth hormone and prolactin from perifused rat pituitary: effect of human pancreatic growth hormone-releasing factor-44.

UNLABELLED: Human pancreatic growth hormone-releasing factor-44 (hpGRF-44) differentially stimulates release of stored and newly synthesized rGH without altering rGH synthesis over 3 h in static in vitro incubation; hpGRF-44 also stimulates release of stored, but not newly synthesized, rPRL. To study the time course of pre-labeled, stored hormone release without pharmacologically interrupting synthesis, the current experiments were performed in perifusion. Fifteen minute pulses of 0.1 to 10 nM hpGRF-44 stimulated stored [3H]rGH release (to 890% of base); 1.0 to 10 nM hpGRF-44 stimulated stored [3H]rPRL release (to 440% of base). Pulses of 0.1 to 1.0 mM (Bu) 2cAMP also stimulated release of [3H]rGH (to 570% of base) and [3H]rPRL (to 410% of base). However, peak [3H]rGH and [3H]rPRL responses to hpGRF-44 required 10 min, while peak responses to (Bu) 2cAMP required 25 min. Continuous hpGRF-44 stimulated an initial surge of stored [3H]rGH release which was not sustained; the diminishing release was not explained by hpGRF-44 degradation. Total radioimmunoassayable (RIA) hormone release roughly paralleled release of stored immunoprecipitable (IPn) hormone. CONCLUSIONS: in pituitary perifusion, hpGRF-44 stimulates release of both stored rGH and rPRL as shown in static incubation, but the response is biphasic: initial rapid release is followed by a progressively lesser response; and the response is both more acute and less well sustained than that resulting from exposure to (Bu) 2cAMP.

Animals↗
PubMed1986

Structural correlates of stimulated and inhibited secretion: electron microscopic observations of somatotrophs in perifused rat pituitary.

The in vitro release of stored intracellular rat growth hormone (rGH) in response to several secretagogues suggests the functional division of rGH storage into at least two 'compartments' or 'pools'. The first is an immediately releasable compartment whose response is brief. The second is a compartment which responds to more prolonged secretory demands. These observations are consistent with either a single, homogeneous population of somatotrophs, each of which exhibits functional compartmentalization of storage, or with heterogeneous populations of somatotrophs, each family of which provides one of the observed responses. We sought anatomical correlates of this functional compartmentalization using a perifusion/morphometric system which permitted examination of the first model while not excluding the second model. We selected for study an established perifusion protocol whose behavior was consistent and whose previous results suggested phases of both filling and emptying of the immediate release pool. Five parallel perifusions of pituitary fragments were run. The fifth perifusion was used to monitor rGH release and to confirm that the experiment had behaved in standard fashion. The first pituitary chamber was dismantled during basal perifusion to obtain tissue for microscopy, the next during exposure to 25 nM SRIF, the third during exposure to both 25 nM SRIF and 1 mM (Bu)2cAMP, and the fourth shortly after the rapid release which followed SRIF withdrawal. Somatotroph granulation was decreased by 54% in the presence of SRIF, and then increased by 45% with the addition of (Bu)2cAMP. The intracellular distribution of granules also fluctuated in relation to the stimulatory and inhibitory secretagogues. In addition, secondary lysosomes increased by 549% during SRIF-induced inhibition of rGH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Differential spontaneous and stimulated in vitro release of newly synthesized or stored rGH and rPRL by pituitaries from rats with hypothalamic lesions.

These experiments were designed to examine which aspects of basal and responsive somatotroph and lactotroph synthesis and release behavior in vitro are functions of in vivo tonic hypothalamic environment. Although we cannot specifically define in vivo hypothalamic tone, we show that spontaneous rates of hormone synthesis and release in vitro, as well as release in response to a secretagogue, are influenced by altered in vivo hypothalamic tone. This work combines in vivo destruction of hypothalamic (ventromedial [VMN] or dorsomedial [DMN]) nuclei with in vitro double-label perifusion to track hormone synthesis and release of newly synthesized and stored hormone. We demonstrate that hormone synthesis rates are greater in DMN-lesioned (DMNL) or sham-operated (SHAM) animals than in VMN-lesioned (VMNL) animals and that DMNL and SHAM synthesis rates fall with time outside the hypothalamic environment. We show that basal release of newly synthesized rGH by DMNL tissue exceeds that of SHAM, while release from VMNL tissue is less than that of SHAM. Accidental placement of small bilateral lesions between and not impinging on either the DMN or VMN nuclei did not alter newly synthesized rGH release but accelerated newly synthesized rPRL release. Although basal fractional release of stored growth hormone and prolactin was the same for the three groups, potassium ion-induced release of stored hormone was similar in DMNL or SHAM tissue, but depressed in VMNL tissue. Thus, the creation of definable hypothalamic damage in a living animal produced specific modifications in in vitro pituitary synthetic/secretory behavior, presumably by reproducibly altering hypothalamic secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Effect of growth hormone-releasing factor-44 upon release of concurrently synthesized hormone by perifused rat pituitary tissue.

We previously reported the differential stimulation of stored and newly synthesized rat (r)GH release by human GH-releasing factor-44 (hGRF-44). Those studies were performed over a 3-h period in a static in vitro incubation system. The present experiments focus on hGRF-44 effects upon release of new hormone (synthesized during tissue stimulation by the secretagogue) and were performed in in vitro perifusion to study the time course of the response. A double label ([14C], [3H]), immunoprecipitation protocol defined hormone release in relation to time of synthesis: intracellular stores of hormone were prelabeled with [14C]; subsequent exposure of prelabeled tissue to continuous concurrent [3H]leucine and 3 nM hGRF-44 defined newly synthesized hormone and associated it with the secretagogue. In a parallel set of experiments, 1 mM (Bu)2cAMP was substituted for hGRF-44. Prolonged exposure to hGRF-44 in perifusion stimulated an initial surge of stored [14C]rGH release which was followed by a rate of [14C]rGH release which declined rapidly but remained suprabasal. [14C]rGH release in response to (Bu)2cAMP was also biphasic, but the initial surge was delayed and the later stimulatory period was better sustained in comparison to responses to hGRF-44. Stimulation of stored [14C] rPRL release by hGRF-44 was observed in perifusion, confirming our observation in the static system. Release of newly synthesized, 3H-labeled rGH was immediately stimulated by either hGRF-44 or (Bu)2cAMP, and that stimulation was maintained throughout exposure to either secretagogue. In contrast, whereas newly synthesized [3H]rPRL release was stimulated by (Bu)2cAMP, its release in response to hGRF-44 resembled that in control experiments. No effect upon hormone synthesis was observed during the 3h of exposure to hGRF-44. In conclusion, these experiments confirm that hGRF-44 differentially stimulates release of both newly synthesized and stored rGH, and demonstrate differential dynamics in the response as well. Specifically, hGRF-44 stimulation of new rGH release is sustained while its effect on stored hormone simultaneously wanes. Further, when expressed as a percent of intracellular hormone available for release, new hormone is released more than 10 times faster than stored hormone. These observations argue for the existence of separate intracellular paths along which newly synthesized and stored hormone are released by the somatotroph. Finally, these data confirm that hGRF-44 stimulates release of stored rPRL without altering release of newly synthesized rPRL.

Animals↗
PubMed1986

Functional substructure of the rat somatotroph immediate release pool: definition by responses to N6,2'-O-dibutyryl cyclic adenosine 3',5'-monophosphate, potassium ion, and/or prostaglandin E1.

Previous results from our laboratory suggest that stored rat GH (rGH) in the pituitary is divisible into at least two functional compartments. An immediate release pool (IRP) responds quickly and can be exhausted. A larger and less labile pool responds continuously to long term stimulation. We previously demonstrated that the sum of IRP rGH discharged by (Bu)2cAMP and potassium ion (K+) in separate experiments exceeds by one third the amount released by the two agents administered simultaneously. This overlap suggested an IRP substructure. We used prelabeled rat pituitary fragments in an in vitro perifusion-immunoprecipitation system to define intracellular hormone storage and to track release of stored rGH and rat PRL (rPRL). We tested three secretagogues: K+ to induce release without altering pituitary cAMP levels, (Bu)2cAMP to introduce cAMP into cells without activating adenylate cyclase, and prostaglandin E1 (PGE1) to produce a temporary, localized cAMP increase through adenylate cyclase activation. Prelabeled tissue in basal perifusion was first exposed to one secretagogue for 90 min. Then, while the first secretagogue was continued, a second secretagogue was added for a second 90-min period. Demonstrable alterations in tissue responses to secretagogues included: K+ diminished PGE1-induced rGH release from the IRP by 69% but had a mixed effect on the response to (Bu)2cAMP; (Bu)2cAMP enhanced K+-induced rGH release from the IRP by 71% but reduced PGE1-induced rGH release by 72%; PGE1 diminished K+-induced rGH release by 13% and (Bu)2cAMP-induced rGH release by 23%; combined K+ and (Bu)2cAMP reduced the rGH response to PGE1 stimulation by 81% whereas prior PGE1 enhanced the response to subsequent combined K+ and (Bu)2cAMP by 16%. We conclude that the somatotroph IRP consists of a K+-sensitive portion which overlaps with, but is not identical to, a (Bu)2cAMP-sensitive portion. The PGE1-sensitive portion of the IRP appears to be roughly equivalent to the shared fraction of the K+- and (Bu)2cAMP-sensitive portions of the IRP. These agents define a similar rPRL compartmentalization. However, the K+-sensitive portions of the somatotroph and lactotroph IRP differ in that the former is larger and expandable, whereas the latter is smaller and appears to be of limited capacity.

Alprostadil↗
PubMed1985

Human pancreatic growth hormone-releasing factor-44 differentially stimulates release of stored and newly synthesized rat growth hormone in vitro.

Effects of synthetic human pancreatic GH-releasing factor-44 (hpGRF-44) on synthesis and release of rat pituitary GH and PRL were examined in vitro in a static incubation system. A double label, specific immunoprecipitation protocol permitted simultaneous study of hormone synthesis as well as release of both stored and newly synthesized hormone. Synthetic hpGRF-44 (0.3 and 3.0 nM) stimulated the release of stored GH 240% beyond the basal level, while simultaneously stimulating the release of newly synthesized GH by 610%. Despite the stimulation of release, hpGRF-44 did not alter GH synthesis (102% of control value). A small but statistically significant increase in release of stored PRL occurred in response to hpGRF-44, while release of newly synthesized PRL and PRL synthesis were unaffected. In contrast, 1 mM (Bu)2cAMP stimulated the release of both newly synthesized and stored GH and PRL. We conclude that hpGRF-44 differentially stimulates GH release from separate intracellular compartments and that the lactotroph may also, under certain conditions, respond to this secretagogue.

Animals↗
PubMed1979

Purification of two spectrin-binding proteins: biochemical and electron microscopic evidence for site-specific reassociation between spectrin and bands 2.1 and 4.1.

Two peripheral proteins of the human erythrocyte membrane that are capable of forming a stable complex with spectrin have been purified. The proteins, band 2.1 (Mr 210,000) and band 4.1 (Mr 82,000), are water soluble and exist as monomers in solution. Both exhibit strong, specific binding to purified spectrin molecules as determined by cosedimentation in sucrose gradients and both enhance binding to spectrin-depleted, inside-out vesicles that have been stripped of bands 2.1 and 4.1. Rotary replicas of bound material reveal site-specific associations among native, but not heat-denatured, molecules.

Binding Sites↗