Biomedical subjects

P G Kent

Publications and source records attributed to P G Kent.

5 recordsLinked to original sources

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↗

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

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↗

PubMed1983

A novel technique for efficient multiple sample dialysis.

Conventional methods for dialyzing numerous samples are either expensive or tedious and inefficient. These disadvantages were overcome through the construction and use of a Plexiglas dialysis sample holder (DSH). Large numbers of dialysis samples having 0.5 to 2.0-ml volumes may be attached to numbered positions on the DSH. Sample identification is greatly simplified and considerable savings in time and material are achieved. Furthermore, the risk of sample spill or mixing during filling or emptying of dialysis sacks, and the risk of leaks in dialysis tubing, are minimized.

Animals↗