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Biomedical subjects

G Aguilera

Publications and source records attributed to G Aguilera.

At least 145 records · Page 8Linked to original sources
PubMed1986

Angiotensin II receptors in the kidney.

Angiotensin II (AngII) receptors have been localized in rat kidney by using the high-affinity agonist analog 125I-labeled [Sar1]AngII as a probe for in vitro autoradiography. Receptors were associated with four morphologically distinct patterns of distribution. First, a high density of receptors occurs in glomeruli. These are diffusely distributed, consistent with a mesangial localization. AngII receptor density shows a cortical gradient, which is highest in superficial and midcortical glomeruli and lowest in juxtamedullary glomeruli. Receptors associated with both superficial and deep glomeruli show down-regulation during low-sodium intake. Second, low levels of tubular AngII binding were seen in the outer cortex. Third, a very high density of AngII receptors occurs in longitudinal bands in the inner zone of the outer medulla in association with vasa recta bundles. Receptors in this site also show down-regulation during low dietary sodium intake. Fourth, a moderate density of receptors occurs diffusely throughout the inner zone of the outer medulla in the interbundle areas. These results suggest that AngII exerts a number of different intrarenal regulatory actions. In addition to the known vascular, glomerular, and proximal tubular effects of AngII, these findings focus attention on possible actions of AngII in the renal medulla where it could regulate medullary blood flow and thereby modify the function of the countercurrent concentrating system.

Angiotensin II↗
PubMed1985

Hormone-induced redistribution of calcium-activated phospholipid-dependent protein kinase in pituitary gonadotrophs.

The distribution of calcium-activated, phospholipid-dependent protein kinase (protein kinase C) between cytosol and membrane fractions was analyzed in cultured pituitary gonadotrophs during treatment with gonadotropin-releasing hormone (GnRH). In pituitary cells purified by centrifugal elutriation, the extent of protein kinase C redistribution during GnRH stimulation was correlated with the enrichment of gonadotrophs. GnRH-stimulated release of luteinizing hormone (LH) from gonadotroph-enriched cells was accompanied by a rapid and dose-dependent decrease in cytosolic protein kinase C and by a corresponding increase in protein kinase C activity in the particulate fraction. Retinal directly inhibited the activity of cytosolic protein kinase C and also attenuated the release of LH from GnRH-stimulated gonadotrophs. These findings, and the ability of GnRH to cause rapid translocation of cytosolic protein kinase C to a membrane-associated form, suggest that hormonal activation of protein kinase C is an intermediate step in the stimulation of pituitary LH secretion by GnRH.

Animals↗
PubMed1985

Quantification of morphological changes in pituitary corticotropes produced by in vivo corticotropin-releasing factor stimulation and adrenalectomy.

Physiological and morphological changes produced by corticotropin-releasing factor (CRF) stimulation in vivo were studied in pituitaries immunocytochemically stained for ACTH. After 48-h ip minipump infusions of 10 or 50 ng/min CRF, serum ACTH levels were increased significantly over values in control groups that included both intact rats and rats exposed to sham abdominal surgery. Correlative morphological changes included a striking increase in corticotrope cell area. This was coupled with an apparent decrease in the percentage of stained cells, probably due to degranulation. The cellular responses were similar to those after adrenalectomy described previously by us and others. Therefore, in a parallel study, additional groups of rats were adrenalectomized and studied 24 and 48 h after the surgery. Even greater changes in serum ACTH, corticotrope cell area, and percentages were observed in the adrenalectomized rats. The difference between the CRF-infused and adrenalectomized groups was probably due to the lack of corticosterone feedback in the latter group. Among the control groups, there were no differences between intact rats and rats exposed to sham abdominal surgery. Rats subjected to sham adrenalectomy, however, showed corticotrope responses similar to those of CRF-infused rats, except that the cells were more densely stained. The present studies thus show dramatic changes in ACTH cell area, extent of staining, and percentages after in vivo CRF stimulation. In all of the experimental groups, an excellent correlation existed between serum ACTH levels and the degree of the morphological changes in the corticotropes.

Adrenalectomy↗
PubMed1985

Regulation of corticotropin-releasing factor (CRF) receptors in the rat pituitary gland: effects of adrenalectomy on CRF receptors and corticotroph responses.

The stimulation of ACTH release from anterior pituitary cells by corticotropin-releasing factor (CRF) is mediated by specific, high affinity receptors with a Ka of 10(9) M-1 for ovine CRF. The relationship between ACTH secretion and CRF receptor activation was analyzed in normal and adrenalectomized rats by comparison of ACTH release with changes in CRF receptors and adenylate cyclase activity. The marked increase in plasma ACTH levels that occurred after adrenalectomy (from 71 to 478 pg/ml after 4 days) was accompanied by a progressive decrease in pituitary CRF receptor concentration [by 29 +/- 1%, 75 +/- 2%, 77 +/- 6%, and 80 +/- 4% (+/- SE) after 1, 2, 3, and 4 days, respectively]. Most of this decrease was due to receptor down-regulation rather than occupancy by endogenous CRF, since high dose infusions of CRF (300-500 ng/min) for 30 min before pituitary membrane preparation reduced CRF-binding sites by only 40%. The marked reduction in CRF receptors after adrenalectomy was accompanied by comparable decreases in maximal CRF-stimulated adenylate cyclase activity and sensitivity to CRF (ED50, 3.8 +/- 2.8 vs. 58 +/- 3.7 X 10-9 M CRF in control and 2-day-adrenalectomized rats, respectively). Fluoride-stimulated adenylate cyclase activity was unchanged at 24 h, but was decreased by 28 +/- 7% at later times. Such decreases in CRF receptors and adenylate cyclase activity in adrenalectomized rats were prevented by dexamethasone treatment. In cultured anterior pituitary cells from 4-day-adrenalectomized rats, CRF-stimulated cAMP production was decreased by 40%. However, in contrast to the decreases in CRF receptors and cAMP production, there was a 3-fold increase in CRF-stimulated ACTH release, with no change in sensitivity to CRF. The ability of corticotrophs to maintain increased ACTH release, in conjunction with reduced CRF receptors and CRF-stimulated adenylate cyclase, indicates that elevated ACTH secretion can be maintained by occupancy and activation of only a small number of CRF receptors. This finding also suggests that synergistic interactions between CRF and other regulators of ACTH release may contribute to the sustained increase in ACTH secretion that follows adrenalectomy.

Adenylyl Cyclases↗
PubMed1984

[3H]nitrendipine binding to adrenal capsular membranes.

The physiologic regulation of aldosterone secretion is dependent on extracellular calcium and appears to be mediated by increases in cytosolic free calcium concentration in the zona glomerulosa cell. A specific role for voltage-dependent calcium channels was suggested by previous studies with the calcium channel antagonist verapamil. We therefore studied the [3H]nitrendipine calcium channel binding site in adrenal capsules. These studies revealed a single class of saturable, high affinity sites with KD = .26 +/- .04 nM and Bmax = 105 +/- 5.7 fmol/mg protein. Specific binding of [3H]nitrendipine was inhibited by calcium channel antagonists with potencies nitrendipine = nifedipine much greater than verapamil, while diltiazem had no inhibitory effect. In the rat, binding sites for [3H]nitrendipine were located in the adrenal capsule and medulla and were undetectable in the zona fasciculata. Physiologic studies with collagenase-dispersed adrenal glomerulosa cells demonstrated that nifedipine selectively inhibited angiotensin-II and potassium-stimulated steroidogenesis. These observations suggest both a pharmacologic and physiologic role for the nitrendipine binding site in aldosterone production.

Adrenal Medulla↗
PubMed1984

Effects of vinblastine in the frog neuromuscular junction during repetitive stimulation.

Vinblastine (10(-5) to 10(-4) M) applied in a Mg-blocked sciatic nerve-sartorius muscle preparation of the frog at the beginning of 20 min of repetitive stimulation of the nerve at 10 Hz, markedly inhibited the facilitation period. There was a smaller increase of end-plate potential amplitude, of quantal content, and of miniature end-plate potential (MEPP) frequency in comparison with that found in experiments without the drug. This depressant effect was more evident when the preparation was preincubated in vinblastine: synaptic responses often disappeared after a few minutes, whereas MEPP frequency attained a maximum at the 5th min. The results suggest a multiple site of action for vinblastine. First, an alteration of both vesicle and plasmalemma membrane, as revealed by the increase of MEPP frequency and by the change of the binomial release features. Second, the drug could damage the intracellular transport system, interfering with the mobilization of the vesicles toward the nerve endings, as shown by the very low or absent facilitation.

Animals↗
PubMed1984

Actions of growth hormone-releasing factor and somatostatin on adenylate cyclase and growth hormone release in rat anterior pituitary.

The interaction of growth hormone-releasing factor (GRF) and somatostatin (SRIF) on adenylate cyclase activity and growth hormone release was investigated in pituitary homogenates and 2-day cultured rat anterior pituitary cells. GRF stimulated growth hormone release by about 3-fold (ED50 1.6 X 10(-12) M) and caused a rapid 15-fold increase in cyclic AMP production (ED50 6.0 X 10(-12) M). The increase in cyclic AMP was due to direct stimulation of adenylate cyclase by GRF, which caused a 4-fold increase in the activity of the enzyme measured in anterior pituitary homogenates. GRF-induced cyclic AMP formation and GRF-stimulated adenylate cyclase activity were maximally inhibited to the extent of about 50% by 10(-8) M somatostatin. In contrast, GRF-stimulated growth hormone release was completely inhibited by somatostatin (ID50 3.2 X 10(-11) M), suggesting a second site of action of somatostatin. These studies demonstrate that GRF stimulates growth hormone release via activation of adenylate cyclase and a rise in intracellular cyclic AMP. In addition, these findings indicate that the inhibitory action of somatostatin on growth hormone release is exerted at two levels, one at the level of adenylate cyclase affecting the production of cyclic AMP, and the other beyond the formation of the nucleotide, at a site which modulates the release of growth hormone from the cell.

Adenylyl Cyclases↗
PubMed1984

Autoradiographic localization of angiotensin II receptors in rat brain.

The 125I-labeled agonist analog [1-sarcosine]-angiotensin II ( [Sar1]AII) bound with high specificity and affinity (Ka = 2 X 10(9) M-1) to a single class of receptor sites in rat brain. This ligand was used to analyze the distribution of AII receptors in rat brain by in vitro autoradiography followed by computerized densitometry and color coding. A very high density of AII receptors was found in the subfornical organ, paraventricular and periventricular nuclei of the hypothalamus, nucleus of the tractus solitarius, and area postrema. A high concentration of receptors was found in the suprachiasmatic nucleus of the hypothalamus, lateral olfactory tracts, nuclei of the accessory and lateral olfactory tracts, triangular septal nucleus, subthalamic nucleus, locus coeruleus, and inferior olivary nuclei. Moderate receptor concentrations were found in the organum vasculosum of the lamina terminalis, median preoptic nucleus, medial habenular nucleus, lateral septum, ventroposterior thalamic nucleus, median eminence, medial geniculate nucleus, superior colliculus, subiculum, pre- and parasubiculum, and spinal trigeminal tract. Low concentrations of sites were seen in caudate-putamen, nucleus accumbens, amygdala, and gray matter of the spinal cord. These studies have demonstrated that AII receptors are distributed in a highly characteristic anatomical pattern in the brain. The high concentrations of AII receptors at numerous physiologically relevant sites are consistent with the emerging evidence for multiple roles of AII as a neuropeptide in the central nervous system.

Angiotensin II↗
PubMed1984

The role of angiotensin II receptors in vascular regulation.

Plasma-membrane receptors for angiotensin II (AII) have been identified in many AII-responsive tissues involved in the control of blood pressure via direct or indirect actions on vascular contractility. The specific, high-affinity receptors for AII in adrenal zona glomerulosa, vascular smooth muscle, kidney, brain, and anterior pituitary gland exhibit generally similar binding properties. However, the AII receptors in adrenal zona glomerulosa and vascular smooth muscle undergo reciprocal regulatory changes during alterations in sodium intake. These appear to be mediated by changes in circulating AII and are accompanied by parallel changes in sensitivity to AII. The AII receptors in the anterior pituitary gland are located in lactotrophs and corticotrophs and mediate the stimulatory actions of AII upon prolactin and ACTH secretion, acting in conjunction with other hypothalamic regulators. The anterior pituitary receptors are not affected by changes in sodium balance or AII infusion, in contrast to adrenal and vascular AII receptors, but exhibit similar ligand-binding properties to the sites present in other tissues. In the brain, AII receptors are present in several discrete regions and are particularly concentrated in the circumventricular organs. During dehydration, AII receptors are increased in the subfornical organ, but show no significant changes in the other circumventricular organs. The increase in subfornical-organ receptors is analogous to the up-regulation of AII sites in the adrenal cortex during sodium deficiency and may have a potentiating action upon the dipsogenic role of AII during dehydration. Mapping of AII receptors of the brain by topical autoradiography has revealed a highly characteristic pattern of distribution in brain regions concerned with drinking, adrenergic control, blood-pressure regulation, and hypothalamic control of pituitary-hormone secretion. In the rat kidney, AII receptors have been localized in the cortex and medulla by topical autoradiography with 125I-[Sar1]AII. The renal cortical receptors appear to be localized in glomeruli, whereas the AII receptors in the renal medulla are distributed diffusely in medullary tissue and also as localized radiating stripes which correspond to the vasa rectae bundles. The location of the renal receptors for AII in cortical and medullary sites emphasizes the multiplicity of actions of the octapeptide upon the individual compartments of the kidney.

Adrenal Glands↗
PubMed1984

Dopaminergic modulation of aldosterone secretion in the rat.

The dopamine antagonist metoclopramide (MCP) has been shown to acutely stimulate aldosterone secretion in vivo. To determine whether a dopaminergic mechanism is involved in the regulation of aldosterone secretion, we examined the effect of minipump infusion of MCP (iv) and/or angiotensin II (AII;sc) upon plasma aldosterone, adrenal capsular AII receptors, and 18-hydroxylase activity in rats maintained on high sodium intake. During normal sodium intake, plasma aldosterone was elevated from 8.3 +/- 1.3 to 35.4 +/- 3.2 ng/dl after 2-day infusion of a nonnatriuretic dose of AII (25 ng/min) and to 15.0 +/- 1.8 ng/dl after the infusion of 1.2 micrograms/min MCP. AII receptors were unchanged by MCP infusion, and rose from 1014 +/- 98 to 1638 +/- 98 fmol/mg after AII infusion. During high sodium intake, the infusion of either AII or MCP alone produced no change in plasma aldosterone or AII receptors. However, after simultaneous infusion of AII and MCP, plasma aldosterone rose from 4.5 +/- 1.2 to 32.5 +/- 2.7 ng/dl, AII receptors increased from 969 +/- 35 to 1607 +/- 280 fmol/mg, and 18-hydroxylase activity, measured as the conversion of corticosterone to aldosterone by isolated mitochondria, rose from 29.5 +/- 1.67 to 40.6 +/- 2.9 pmol/mg . min. These adrenal responses induced by the combined treatment with AII and MCP were similar to the effects of AII infusion during normal sodium intake, indicating that MCP exerts a permissive action upon the trophic effects of AII on the adrenal cell during high sodium intake. These actions of MCP were completely abolished by the simultaneous infusion of dopamine (2 micrograms/min), suggesting that the effects of MCP on adrenal function are due to its dopaminergic antagonist properties. In collagenase-dispersed adrenal glomerulosa cells, only supraphysiological concentrations of dopamine in the incubation medium (10-100 microns) inhibited basal, AII-stimulated, and ACTH-stimulated aldosterone production, and these inhibitory effects were not reversed by high concentrations of MCP. Also, MCP itself inhibited both basal and stimulated aldosterone production. These results suggest that the stimulatory actions of MCP in vivo are exerted through liberation of other local regulators, rather than directly upon the adrenal glomerulosa cell. These findings have defined a mechanism by which the primary regulatory action of AII upon aldosterone secretion can be modulated during high sodium intake by dopaminergic inhibition of adrenal glomerulosa function.

Adrenal Glands↗
PubMed1984

Inhibitory actions of calmodulin antagonists on steroidogenesis in zona glomerulosa cells.

The stimulation of aldosterone (Aldo) production in the adrenal glomerulosa cell by angiotensin II (AII) and ACTH is highly dependent on calcium. To determine the role of calmodulin (CM) as a regulator of intracellular calcium during hormonal activation of steroidogenesis, the actions of a series of CM inhibitors on the stimulation of Aldo biosynthesis by AII, the calcium ionophore A23187, ACTH, and cAMP were examined in isolated adrenal glomerulosa cells. The CM antagonists, pimozide, W7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide] and W5 [N-(6-aminohexyl)-1-napthalenesulfonamide] caused dose-dependent inhibition of hormone-stimulated Aldo production, in proportion to their reported binding affinities for CM. The maximum inhibitory concentration (5 microM) of the most potent CM antagonist, pimozide, had no effect on the conversion of progesterone to Aldo. However, submaximal inhibitory concentrations of W7 and W5 also reduced conversion of progesterone to Aldo, indicating that their inhibitory action is not only due to their CM antagonist properties. The relative sensitivities of the stimuli of Aldo release to inhibition by all three CM inhibitors were A23187 = AII greater than ACTH greater than 8-bromo-cAMP (8-Br-cAMP). Aldo responses to ACTH were more sensitive to inhibition by pimozide than those to 8-Br-cAMP, suggesting that ACTH-induced cAMP formation is also dependent on CM. Pimozide (5 microM) completely inhibited the Aldo responses to AII and A23187, whereas the Aldo responses to ACTH and 8-Br-cAMP were only partially inhibited. At submaximal inhibitory concentrations, pimozide caused a decrease in the maximum response to AII without changing the concentration of the peptide required for half-maximum stimulation of Aldo production. The inhibition of Aldo production by pimozide was accompanied by parallel inhibition of pregnenolone accumulation measured in the presence of cyanoketone. No effect of pimozide (5 microM) was observed on the binding of 125I-AII to adrenal glomerulosa cells, placing the CM-dependent site between the receptor and the side-chain cleavage enzyme. These findings indicate that CM-mediated regulation is essential for the steroidogenic response to calcium ionophore and AII, but is only partially required for the responses to ACTH and 8-Br-cAMP.

Adrenal Cortex↗
PubMed1983

Mechanisms of action of corticotropin-releasing factor and other regulators of corticotropin release in rat pituitary cells.

The role of cyclic AMP in the stimulation of corticotropin (ACTH) release by corticotropin-releasing factor (CRF), angiotensin II (AII), vasopressin (VP), and norepinephrine (NE) was examined in cultured rat anterior pituitary cells. Synthetic CRF rapidly stimulated cyclic AMP production, from 4- to 6-fold in 3 min to a maximum of 10- to 15-fold at 30 min. Stimulation of ACTH release by increasing concentrations of CRF was accompanied by a parallel increase in cyclic AMP formation, with ED50 values of 0.5 and 1.3 nM CRF for ACTH and cyclic AMP, respectively. A good correlation between cyclic AMP formation and ACTH release was also found when pituitary cells were incubated with the synthetic CRF(15-41) fragment, which displayed full agonist activity on both cyclic AMP and ACTH release with about 0.1% of the potency of the intact peptide. In contrast, the CRF(21-41) and CRF(36-41) fragments were completely inactive. The other regulators were less effective stimuli of ACTH release and caused either no change in cyclic AMP (AII and VP) or a 50% decrease in cyclic AMP (NE). Addition of the phosphodiesterase inhibitor, methylisobutylxanthine, increased the sensitivity of the ACTH response to CRF but did not change the responses to AII, VP, and NE. In pituitary membranes, adenylate cyclase activity was stimulated by CRF in a dose-dependent manner with ED50 of 0.28 nM, indicating that the CRF-induced elevation of cyclic AMP production in intact pituitary cells is due to increased cyclic AMP biosynthesis. The intermediate role of cyclic AMP in the stimulation of ACTH release by CRF was further indicated by the dose-related increase in cyclic AMP-dependent protein kinase activity in pituitary cells stimulated by CRF with ED50 of 1.1 nM. These data demonstrate that the action of CRF on ACTH release is mediated by the adenylate cyclase-protein kinase pathway and that the sequence requirement for bioactivity includes the COOH-terminal 27 amino acid residues of the molecule. The other recognized regulators of ACTH release are less effective stimuli than CRF and do not exert their actions on the corticotroph through cyclic AMP-dependent mechanisms.

Adrenocorticotropic Hormone↗
PubMed1983

Properties and regulation of high-affinity pituitary receptors for corticotropin-releasing factor.

Specific receptors for corticotropin-releasing factor (CRF) were identified in the rat anterior pituitary gland by binding studies with 125I-Tyr-CRF. Binding of the labeled CRF analog to pituitary particles was rapid and temperature-dependent, and reached steady state within 45 min at 22 degrees C. The CRF binding sites were saturable and of high affinity, with dissociation constant (Kd) of 0.76 X 10(-9) M. Pituitary binding of 125I-Tyr-CRF was inhibited by CRF, Tyr-CRF and the active 15-41 fragment of CRF, but not by the inactive 21-41 CRF fragment and unrelated peptides. The binding-inhibition potencies of the CRF peptides were similar to their activities as stimuli of adrenocorticotropic hormone (ACTH) release. The high-affinity CRF sites were markedly reduced in adrenalectomized rats, and this change was reversed by dexamethasone treatment. These data indicate that the high-affinity CRF sites demonstrated in the anterior pituitary are the functional receptors which mediate the stimulatory action of the peptide on ACTH release, and that CRF receptors are down-regulated during increased secretion of the hypothalamic hormone.

Adrenalectomy↗
PubMed1983

Regulation of aldosterone secretion during altered sodium intake.

The interactions of the renin-angiotensin system with other factors in the regulation of aldosterone secretion were analyzed during altered sodium in the rat. During sodium restriction, the rise in aldosterone one secretion was accompanied by trophic changes in the adrenal glomerulosa zone including increased angiotensin II receptors and enzymes of early and late steps in the aldosterone biosynthetic pathway. All these effects of sodium restriction were reproduced by infusion of angiotensin II, and could be prevented by administration of the converting enzyme inhibitor, SQ 14,225. These findings indicate that the adrenal secretory and trophic responses to sodium restriction are mediated by angiotensin II. In hypophysectomized rats, the basal activities of the enzymes of the early aldosterone biosynthetic pathway were reduced, contributing to the blunted aldosterone responsiveness to sodium deficiency. However, sodium restriction for 6 days significantly increased adrenal glomerulosa angiotensin II receptors and enzymes of the early and late aldosterone biosynthetic pathway, indicating that the pituitary gland is not necessary for the adrenal effects of angiotensin II. In contrast to the prominent glomerulotropic actions of angiotensin II in rats on normal or low sodium intake, infusion of angiotensin II during high sodium intake did not increase blood aldosterone, angiotensin II receptors, or 18-hydroxylase activity, indicating that the trophic actions of the octapeptide are determined by the state of sodium balance. In recent studies, other factors including potassium, dopamine and somatostatin have been shown to potentiate or inhibit the actions of angiotensin II on the adrenal gland. The ability of such factors to influence the effects of angiotensin II could serve as a protective mechanism to modulate aldosterone responses to angiotensin II when elevations in the circulating level of the peptide occur in the absence of sodium deficiency.

Adrenal Cortex↗
PubMed1983

Characteristics and regulation of angiotensin II receptors in pituitary, circumventricular organs and kidney.

Receptors for angiotensin II (AII) have been identified and characterized in many AII-responsive tissues. Those in the adrenal zona glomerulosa and vascular smooth muscle undergo dynamic regulation which appears to be mediated by changes in circulating AII, and is followed by parallel changes in sensitivity to AII. Pituitary AII receptors are mainly located in lactotrophs and corticotrophs, where they mediate specific actions of AII upon prolactin and ACTH secretion, acting in conjunction with other hypothalamic regulators. In contrast to adrenal and vascular AII receptors, those in the anterior pituitary are not affected by changes in salt balance or AII infusion. In the brain, AII receptors were increased in the subfornical organ during dehydration, but show no significant changes in the other circumventricular organs. The increase in subfornical organ receptors resembles the up-regulation of AII sites which occurs in the adrenal cortex during sodium deficiency, and could play a role in potentiating the dipsogenic effect of AII in dehydration. In the rat kidney, AII receptors have been localized in both cortex and medulla by autoradiography with 125I-[Sar1]AII. While the renal cortical receptors appear to be localized to glomeruli, the most striking feature of these studies is the abundance of specific, high-affinity AII receptors in the renal medulla.

Adrenal Glands↗
PubMed1982

Pituitary somatostatin receptors. Characterization by binding with a nondegradable peptide analogue.

Somatostatin receptors in the rat pituitary gland were characterized by binding analysis with a radioiodinated high affinity somatostatin analogue, 125I-Tyr1[D-Trp8]somatostatin. Receptor binding of this derivative reached equilibrium at 30 min and was maintained at a plateau for at least 60 min. Two L-Trp8- labeled somatostatin analogues. 125I-Tyr1- and [125I-Tyr11]somatostatin, displayed less stable and lower specific uptake and higher nonspecific binding. In contrast to the rapid degradation of the L-Trp8 ligands during binding assay, 125I-Tyr1]D-Trp8]somatostatin retained more than 80% of its binding activity after 90 min of incubation with pituitary particles. Pituitary particles bound 125I-Tyr1]D-Tyr8]somatostatin with high affinity (Ka = 8.6 +/- 1.2 X 10(9) M-1) and capacity of 54.4 +/- 2.6 fmol/mg. These binding sites showed specificity for the native peptide and its active analogues, and other peptide hormones, including angiotensin II, thyrotropin-releasing hormone, vasopressin, oxytocin, substance P, and gonadotropin-releasing hormone, did not inhibit tracer binding. A good correlation was observed between the binding affinities of several somatostatin analogues and their potencies as inhibitors of growth hormone release in rat pituitary cells. These findings emphasize the physiological importance of the pituitary somatostatin receptor in mediating the inhibitory action of the peptide on growth hormone release. The use of Tyr1[d-Trp8]somatostatin as a labeled ligand permits accurate determinations of the binding affinity and concentration of receptors for somatostatin in the normal pituitary gland and provides a basis for further studies of somatostatin receptor regulation and receptor-mediated cellular effects of the tetradecapeptide.

Animals↗
PubMed1982

Characterization of angiotensin II receptors in the anterior pituitary gland.

Specific and high affinity binding sites for angiotensin II were demonstrated in the anterior pituitary gland by binding studies with [125I] iodoangiotensin II. The binding properties of the pituitary receptors were similar to those of angiotensin II receptors present in the adrenal gland. The concentration of binding sites in rat anterior pituitary (293 +/- 50 fmoles/mg protein) was less than in the adrenal gland, but was much greater than in smooth muscle. Angiotensin II receptors were identified in the anterior pituitary tissue of mature and immature animals of both sexes, and in species including rat, rabbit and dog. No binding of angiotensin II was detected in posterior pituitary homogenates, or in GH3 pituitary tumor cells. Collagenase-dispersed anterior pituitary cells also contained specific binding sites for angiotensin II, with equilibrium binding constant (Ka) of 3.6 x 10(9) M-1. The presence of specific high-affinity angiotensin II receptor in the anterior pituitary gland provides a mechanism by which angiotensin-like peptides could modulate the process of pituitary hormone secretion.

Angiotensin II↗