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Biomedical subjects

K J Catt

Publications and source records attributed to K J Catt.

At least 289 records · Page 16Linked to original sources
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

Development of heterologous down-regulation of lactogen receptors in the rat testis.

Gonadotropin-induced loss (down-regulation) of testicular lactogen receptors was studied in 5-60-day-old rats. An i.m. injection of 600 IU/kg of hCG elicited in 5-day-old animals a 38-56% increase in testicular lactogen binding, measurable between 6 and 72 h after the hormone injection. In contrast, at the age of 60 days the same hCG dose decreased lactogen receptors by 75% at 24 h, which loss recovered in 2-3 days. When the amount of lactogen receptors was measured 24 h after the hCG injection (600 IU/kg) at different ages, the binding increased on average by 50% between ages 5 and 20 days, no effect on binding was seen at day 30, and a loss of binding by 50% was evident in animals of 40 days of age and older. The present results indicate that the plasma-membrane events elicited by gonadotropin binding to neonatal Leydig cells are clearly different from those occurring in the adult, and that down-regulation and functional coupling of LH and lactogen receptors are accompaniments of functional differentiation of the Leydig cell during pubertal maturation.

Age Factors↗
PubMed1983

Absence of gonadotropin-induced desensitization of testosterone production in the neonatal rat testis.

The formation of testosterone and some of its precursors (pregnenolone, progesterone, 17-hydroxyprogesterone and androstenedione) was studied in response to hCG stimulation in neonatal (5-day-old) and adult (60-day-old) male rats. Evidence for a biphasic testosterone response was observed at both ages, with a sharp increase within the first hours, and a secondary peak at 2-3 days after the hormone injection, when monitored by intratesticular and serum steroid measurements. The decreased testosterone production between the two peaks coincided in the adult animals with a marked increase of progesterone and 17-hydroxyprogesterone production, in keeping with the known gonadotropin-induced lesions of testicular androgen production. In contrast, no increase in C21-form testosterone precursors could be observed in the neonatal rat. When in vitro testicular production of cAMP, testosterone and progesterone was studied at the two ages 24 h after the hCG injection, a decrease in extracellular cAMP and testosterone but an increase in progesterone was observed in the adult testis. In the neonate, cAMP production was decreased, but testosterone production stayed high, and progesterone production increased only marginally. The present results indicate that the adult-type steroidogenic lesions following in vivo hCG stimulation, resulting in decreased testosterone production and accumulation of C21 steroid precursors, are not operative during the fetal-neonatal growth phase of rat testis Leydig cells.

17-alpha-Hydroxyprogesterone↗
PubMed1983

Inhibitory actions of a gonadotropin-releasing hormone agonist on ovarian follicle-stimulating hormone receptors and adenylate cyclase in vivo.

The regulation of ovarian gonadotropin-sensitive adenylate cyclase and FSH receptors was studied in hypophysectomized diethylstilbestrol-primed rats treated with FSH and/or the potent GnRH agonist [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa). The animals were treated with 7.5 micrograms ovine FSH twice daily for 2 days, either alone or with 10 micrograms GnRHa. FSH-stimulated adenylate cyclase activity was augmented by 2.5- to 3.5-fold in the presence of 5'-guanyl-imidodiphosphate. Adenylate cyclase responses to FSH were almost completely abolished by GnRHa treatment in ovarian homogenates from control animals and rats treated with FSH. This inhibition was receptor specific, since GnRHa did not block adenylate cyclase stimulation by prostaglandin E2 or isoproterenol. No inhibition of 5'-guanyl-imidodiphosphate- or sodium fluoride-stimulated adenylate cyclase activity was noted after any hormone treatment. When GnRHa treatment was initiated at 12, 24, or 36 h during the 2-day period of FSH treatment, inhibition of both FSH- and LH-stimulated adenylate cyclase was observed in ovaries collected at 48 h. Whereas FSH treatment increased the ovarian FSH receptor concentration by more than 100%, concomitant treatment with GnRHa prevented this increase and reduced FSH receptors to 60% of the control level. Treatment with GnRHa alone caused a 65% decrease in FSH receptor levels below the untreated control values. Histological analysis of hormone-treated ovaries indicated that FSH stimulated follicle growth and antrum formation, but caused little luteinization. GnRHa did not completely prevent the effects of FSH on follicle growth, but did induce degeneration and premature cleavage of ova. GnRHa alone suppressed the diethylstilbestrol-stimulated mitotic activity, slightly increased degenerative changes in granulosa cells, and caused oocyte cleavage and premature antrum formation. These findings demonstrate that GnRHa inhibits FSH-dependent adenylate cyclase by a mechanism involving the loss of binding sites for FSH. It is also evident that only short term exposure to GnRHa is necessary for expression of the inhibitory action of the peptide upon FSH- and LH-stimulated adenylate cyclase.

Adenylyl Cyclases↗
PubMed1983

Inhibition of pituitary gonadotropin secretion by 4-aminopyrazolo(3,4-d) pyrimidine.

The reduction of plasma testosterone (T) in male rats treated with 4-aminopyrazolo(3,4-d)pyrimidine (4-APP) has been recently shown to be associated with a fall in plasma LH, and appears to be secondary to this impairment of gonadotropin secretion rather than to the decrease in lipoprotein cholesterol caused by the adenine analog. The effects of 4-APP on pituitary function and the mechanism of the fall in gonadotropin secretion were analyzed in adult male rats treated ip with 5, 10, 25, and 50 mg 4-APP/kg BW for 3 days. Twenty four hours later, serum cholesterol levels were reduced by 68 +/- 5% (mean +/- SE) in animals treated with 5 mg 4-APP/kg BW and by up to 84 +/- 1% after higher doses. Basal levels of serum T were not affected by 5 mg/kg APP but were significantly reduced by higher doses (P less than 0.05). Serum T responses to human CG (100 IU) stimulation in APP-treated rats were reduced in absolute magnitude, but were enhanced in terms of percentage increase above baseline. The three highest doses of 4-APP reduced serum levels of LH (51-79%) and FSH (21-39%). However, serum gonadotropin responses to GnRH stimulation were augmented by 32 +/- 9% for LH and 27 +/- 12% for FSH after 4-APP treatment. Serum levels of TSH were significantly (P less than 0.05) reduced by 25 and 50 mg/kg 4-APP and serum PRL was lowered by only the higher dose. Serum GH was lowered and ACTH increased by 5 mg/kg 4-APP. The pituitary contents of LH, FSH, and TSH were unchanged after 4-APP treatment, but PRL and GH contents were slightly but significantly increased (P less than 0.05). Pituitary receptors for GnRH (88 +/- 14 fmol/mg protein) were reduced by in vivo treatment with 25 and 50 mg/kg 4-APP to 52 +/- 5 and 57 +/- 7 fmol/mg, but not by 10 mg/kg 4-APP. No change in pituitary GnRH receptor content was observed after 48-h exposure to 10(-7) or to 10(-5) M 4-APP in vitro. The medial hypothalamic GnRH content was unchanged by 4-APP treatment. The dissociated effects of 4-APP on serum cholesterol and T levels, and the maintenance of T responses to human CG, provide further evidence that testicular androgen biosynthesis is not solely dependent on circulating cholesterol. The greater sensitivity of pituitary gonadotropins to 4-APP inhibition is evidence for a selective action of this drug on pituitary hormone release in vivo. Although the hypothalamic content of GnRH was unaltered by 4-APP treatment, the decrease in pituitary GnRH receptors observed in vivo, together with the fall in circulating LH and FSH and retention of gonadotropin responses to GnRH stimulation, suggest that the primary effect of 4-APP is to inhibit GnRH synthesis and/or release from the hypothalamus.

Adenine↗
PubMed1983

Calcium dependence of the inhibitory effect of gonadotropin-releasing hormone on luteinizing hormone-induced cyclic AMP production in rat granulosa cells.

The role of calcium in the inhibitory action of the GnRH superagonist, [D-Ala6]des-Gly10-GnRH N-ethylamide (GnRHa), on LH-stimulated cAMP production was studied in cultured granulosa cells obtained from immature hypophysectomized diethylstilbestrol (DES)-implanted rats. After culture for 48 h with FSH to induce LH receptors, cells were incubated for 2 h with LH or LH plus GnRHa. In this system, the cAMP response to LH was independent of extracellular calcium. In the presence of 0.25 to 1 mM extracellular calcium, 10(-8) M GnRHa caused a 15 to 40% inhibition of LH-stimulated cAMP production. Omission of extracellular calcium completely abolished the inhibitory effect of GnRHa upon LH-induced cAMP production. The inhibitory effects of GnRHa on prostaglandin E2 (PGE2) and isoproterenol-induced cAMP productions were also markedly reduced in the absence of extracellular calcium. Addition of the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX), reversed the inhibitory action of GnRHa on LH-induced cAMP production. These results demonstrate that extracellular calcium is necessary for the acute inhibitory action of GnRHa upon LH-induced cAMP production in cultured rat granulosa cells, and indicate that increased degradation of cAMP may be a contributing factor for this effect of GnRHa.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Hormonal activation of phospholipid methyltransferase in the Leydig cell.

Hormonal stimulation of purified rat Leydig cells with hCG caused a 2-fold increase in phospholipid methyltransferase activity within 10 min. This effect of gonadotropin was concentration dependent, with maximal activation of methyltransferase at 10(-12) M hCG, and was reproduced by 8-bromo-cAMP. Hormonal activation of phospholipid methyltransferase caused an increase in the maximum velocity of the enzyme, without changing the Km for S-adenosylmethionine. Analysis of the pattern of radiolabeled phospholipids from Leydig cells showed that the incorporation of methyl groups and the increase in phospholipid methylation stimulated by 8-bromo-cAMP occurred mainly in phosphatidyl-N-monomethylethanolamine. The rapid and highly sensitive increase in phospholipid methylation in hCG-stimulated Leydig cells is consistent with a role of methyltransferase in the hormonal activation mechanism probably at a step subsequent to cAMP production.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Granulosa cell differentiation in vitro: induction and maintenance of follicle-stimulating hormone receptors by adenosine 3',5'-monophosphate.

Granulosa cell differentiation is stimulated in vitro by FSH and other agents that increase cAMP production. To determine if alterations in FSH receptors are associated with cAMP-mediated granulosa cell maturation, FSH-binding sites were measured during culture of undifferentiated granulosa cells from hypophysectomized diethylstilbestrol-implanted rats. FSH receptors decreased rapidly in the absence of stimulatory ligands, with loss of 75% and 90% of the FSH-binding activity from freshly prepared cells after 24 and 48 h, respectively. The decline in FSH receptors during culture was accompanied by a corresponding decrease in cAMP responses to added FSH. In cells cultured with FSH, the available FSH receptor content fell to 15% after 8 h, then rose to 25% of the initial receptor levels from 24-48 h of culture. Cells treated with 8-bromo-cAMP or choleragen for 48 h retained about 40% and 90%, respectively, of their initial FSH-binding activity. Although choleragen did not prevent the 60-70% fall in FSH binding during the first 6 h of culture, it increased receptors 2.5-fold from 12-48 h. Also, the addition of choleragen after 3, 6, or 12 h of culture elevated FSH receptors at 48 h in proportion to the amount of cAMP produced. The FSH receptors induced by choleragent treatment were functionally active, as shown by their ability to mediate FSH-stimulated cAMP production. A GnRH agonist prevented the choleragen-induced rise in FSH receptors and cAMP accumulation from 24-48 h of culture. Scatchard analysis revealed a single population of FSH receptors after all treatments, with association constant of 5 X 10(9) M-1. Freshly prepared cells contained approximately 1600 FSH binding sites/cell, while treatment with choleragen or FSH for 48 h restored receptor levels to 1150 and 500 sites/cell, respectively. These results indicate that the expression of functional FSH receptors during granulosa cell maturation is mediated by cAMP.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1983

Comparison of oestrogen and GnRH agonist analogue-induced inhibition of the pituitary-testicular function in rat.

The purpose of the present study was to compare the inhibitory effects of oestrogen and a gonadotrophin releasing hormone agonist analogue (GnRH-A) on the pituitary-testicular function of adult rats. Animals were treated with sc injections of oestrogen (diethylstilboestrol, DES, 5 or 50 micrograms/kg body weight/day) or a gonadotrophin releasing hormone agonist analogue. [(D-Ser-(tBu)6)des-Gly10-GnRH N-ethylamide, GnRH-A, 0.4 or 4 micrograms/kg/day] up to 12 days. Serum LH (24 h after the last hormone injection) decreased by 83% in 3 days with DES, but was unchanged during 12 days of GnRH-A treatment. Serum testosterone (T) decreased by 98% during DES treatment, and also clearly but less profoundly, by 89% with GnRH-A. Maximal decrease in the weights of the ventral prostate and seminal vesicles were 73-78% with DES-treatment, but clearly slower, and to a lesser extent, with GnRH-A (33-41%). Testicular weights decreased consistently (up to 41%) with GnRH-A treatment only. DES decreased the content of testicular LH receptors by 40% in 12 days whereas GnRH-A caused a loss of 97% in LH binding. Testicular lactogen receptors decreased to similar extents (by 68-78%) with both treatments. A clear increase in serum progesterone/T ratio was observed with both types of treatment, suggesting blockade of steroidogenesis at the C21 steroid level. These findings suggest that the antigonadal actions of oestrogen in the intact animal are largely due to a decrease of circulating gonadotrophin levels, and that those of GnRH-A are predominately due to Leydig cell LH-receptor down-regulation and steroidogenic lesions, induced by transiently elevated gonadotrophin levels. The inhibitory effects of oestrogen on testicular function appeared to be faster and more complete that those of GnRH-A in the present short-term experiments.

Animals↗
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

Yeast mating pheromone activates mammalian gonadotrophs: evolutionary conservation of a reproductive hormone?

alpha-Factor, a tridecapeptide mating pheromone of yeast (Saccharomyces cerevisiae), has extensive sequence homology with the hypothalamic decapeptide gonadotropin-releasing hormone (GnRH). Both synthetic and natural preparations of alpha-mating factor were found to bind specifically to rat pituitary GnRH receptors and to stimulate the release of luteinizing hormone from cultured gonadotrophs. The ability of the yeast pheromone to reproduce the biological actions of GnRH in the mammalian pituitary gland indicates that the structural and functional properties of GnRH-related peptides may have been highly conserved during evolution.

Animals↗
PubMed1982

Luteinizing hormone receptors and gonadotropic activation of purified rat Leydig cells.

Specific receptors and metabolic responses to luteinizing hormone (LH) were analyzed in testicular Leydig cells purified by centrifugation of collagenase-dispersed rat interstitial cells on density gradients of 14-32% Metrizamide. This procedure separated the interstitial cells into an upper, poorly responsive fraction and a lower, more dense population with high LH receptor content and prominent cyclic AMP and testosterone responses of gonadotropic stimulation. The upper layer consisted of morphologically heterogeneous and extensively vacuolated cells, of which relatively few were structurally identifiable as Leydig cells. The lower layer was comprised of almost homogenous Leydig cells when analyzed by electron microscopy and autoradiography, and sedimented as two adjacent bands with similar hormonal responses and densities of 1.085 and 1.105 g/cm3. The lighter and less responsive cell population appeared to result from the presence of damaged cells in the interstitial cell preparation and could be removed during density gradient isolation of the homogeneous and biologically active Leydig cell fraction. The more dense and active Leydig cell population retained hormonal responsiveness during culture for 24 h and showed loss of LH receptors and low concentrations of gonadotropin in vitro. These findings emphasize the importance of appropriate fractionation of rat interstitial cells to isolate the structurally intact and functionally active population of Leydig cells during studies on LH receptors and section in the testis.

Animals↗
PubMed1982

Hormonal regulation of gonadotropin receptors and steroidogenesis in cultured fetal rat tests.

Gonadotropic activation of the adult rat testis in vitro and in vivo is followed by down-regulation of luteinizing hormone receptors and decreased androgen responses to subsequent hormonal stimulation. In contrast, treatment of cultured fetal testes with gonadotropins and dibutyryl adenosine 3',5'-monophosphate enhanced steroidogenic responsiveness and did not cause the luteinizing hormone-receptor loss and desensitization that is characteristic of the adult gonad. The analysis of gonadotropin receptors and action in cultured fetal testis cells facilitates developmental studies of gonadal function, and has revealed significant differences in the responses of fetal and adult Leydig cells to gonadotropic regulation.

Animals↗