The adrenal and vascular effects of angiotensin II and III in sodium depleted rats

The effects of angiotensin II and angiotensin III on mean arterial pressure, serum aldosterone, and serum corticosterone were studied in normal and sodium depleted, conscious rats. In normal rats, angiotensin III was 76% (p > 0.10) as potent as angiotensin II on aldosterone release but only 31% (p < 0.001) as potent on blood pressure. Following sodium depletion, the pressor responses to both angiotensin II and III were reduced (p < 0.001) (65% and 86% respectively). In addition, the release of aldosterone by both peptides was potentiated by sodium depletion as indicated by an increase in the slope of the dose-response curves. However, in the sodium depleted rats, angiotensin III was only 20% (p < 0.001) as potent as angiotensin II in stimulating aldosterone release. Small changes in serum corticosterone were noted following infusions of both peptides, but unlike the case with aldosterone, sodium depletion did not alter the serum corticosterone responses to the peptides. These $\text{in}$$\text{vivo}$ experiments taken with $\text{in}$$\text{vitro}$ studies support the interpretation that angiotensin III could function to control aldosterone release in altered sodium states either as a circulating hormone if present in concentrations far in excess of those of angiotensin II or as a local hormone formed in the adrenal from angiotensin II.     

Trilostane,an orally active inhibitor of steroid biosynthesis

Trilostane is a competitive inhibitor of 3β-hydroxysteroid dehydrogenase. $\text{In}$$\text{vitro}$, the drug inhibits conversion of pregnenolone to progesterone but does not alter conversion of cholesterol to pregnenolone nor progesterone to corticoid hormones. When given orally to rats, trilostane inhibits corticosterone and aldosterone production and elevates circulating levels of pregnenolone at doses lower than those that produce adrenal hypertrophy or inhibit gonadal steroidogenesis.     

The participation of corticosterone in luteinizing hormone releasing hormone (LH-RH) action on luteinizing hormone (LH) release from anterior pituitary cells in vitro

Corticosterone alone was not able to stimulate release of luteinizing hormone (LH) from anterior pituitary cells $\text{in}$$\text{vitro}$, but corticosterone in combination with luteinizing hormone releasing hormone (LHRH) augmented the release of LH into the culture media. These results may indicate that corticosterone may have the capacity to activate membrane receptors for LHRH in the gonadotrophs.     

Effects of naloxone on the secretion of prolactin and corticosterone induced by 5-hydroxytryptophan and a serotonergic agonist, mCPP

The effects of naloxone, an opiate “pure” receptor antagonist, on the release of prolactin and corticosterone in the rat were studied following the administration of the serotonin precursor 5-hydroxytryptophan or the serotonin receptor agonist (?) -$\text{m}$-chloropnehylpiperazine. Naloxone clearly antagonizes the release of prolactin induced by 5-hydroxytryptophan administered alone at a dosage of 50 mg/Kg/b.wt. or at dosage of 30 mg/Kg/b.wt. preceded 60 minutes before injection by the administration of the serotonin uptake blocker fluoxetine. The opiate antagonist does not modify the increase in blood level of prolactin induced by (?) ?$\text{m}$-chlorohenylpiperazine. Naloxone itself does not reduce the increase in plasma level of corticosterone induced by 5-hydroxytryptophan, 5-hydroxytryptophan +fluoxetine or (?)?$\text{m}$-chlorophenylpiperazine.The results suggest that endogenous opioids may be involved in the increase in serum level of prolactin induced by 5-hydroxytryptophan and also indicate the existence of different serotonergic neurotransmitter circuits capable of modulating the release of prolactin and corticosterone. A mutual interplay between serotonergic and opiate neurons may be involved in controlling the release of prolactin, but such an interplay does not seem to occur in the secretion of corticotrophin-releasing hormone.     

Inhibitory action of norepinephrine on the induction of tryptophan-2,3-dioxygenase by cortisol: mediation by the alpha-receptor.

Induction of hepatic tryptophan-2,3-dioxygenase in rats by cortisol or corticosterone was inhibited on treatment with norepinephrine. The β-adrenergic blockers showed a small potentiating effect of the norepinephrine-mediated inhibition. The α-adrenergic blockers significantly reversed this inhibition, suggesting that norepinephrine acts $\text{via}$ the α-receptor in inhibition of the cortisol-mediated induction of this enzyme.     

Effect of caerulein on plasma corticosterone concentration in the rat

Intraperitoneal injection of caerulein produced a pronounced increase in plasma corticosterone levels in intact rats. Since this effect was not observed in hypophysectomized rats, it is assumed that the peptide does not affect the adrenal gland directly. Intracerebroventricular injection of caerulein was also ineffective in stimulating corticosterone secretion, and $\text{in vitro}$ experiments for ACTH release indicated that caerulein could not affect pituitary tissue itself. The fact that the effect of caerulein disappeared after subdiaphragmatical vagotomy suggests that the action site is at a peripheral level, but not in the central nervous system.     

Effect of jet aircraft noise upon in vitro adrenocortical response to ACTH in feral Mus musculus.

Paired adrenals from feral male $\text{Mus musculus}$ trapped from fields adjacent to the Memphis (TN) International Airport and from suitable control areas were incubated in the presence or absence of ACTH. Incubation media were assayed fluorometrically for corticosterone. Control animals exhibited lower basal secretion rates of corticosterone when compared to their noise exposed counterparts. However, ACTH elicited a significantly greater increase in corticosterone secretion in controls as compared to the noise exposed group. The data suggest a noise related decline in adrenal cortical responsiveness to ACTH.     

Interactions of thyrotropin releasing hormone and morphine sulfate in rodents.

Thyrotopin releasing hormone (TRH) produces “wet dog shakes” in rats similar to those observed during morphine withdrawal. The shaking behavior precipitated by morphine abstinence can be exacerbated by TRH administration while the other components of the morphine withdrawal syndrome remain unchanged. Morphine, chlorpromazine, apomorphine, and Δ⁹-tetrahydrocannabinol effectively block shakes induced by either TRH administration or morphine withdrawal. These results suggest the possibility that endogenous TRH may be associated with the “wet dog shakes” observed as a portion of morphine's abstinence syndrome in rats. However, TRH is unable to alter the stereospecific binding of morphine $\text{in}$$\text{vivo}$ or $\text{in}$$\text{vitro}$, and naloxone fails to potentiate the number of TRH-induced shakes. TRH has no antinociceptive properties, and it cannot alter those of morphine. These data suggest that more than one neuromechanism may be responsible for shaking behavior in rats.     

Isolated adrenal cortex cells: ACTH agonists, partial agonists, antagonists; cyclic AMP and corticosterone production

Isolated adrenal cortex cells respond to the addition of ACTH_1–39 or analogs with increased production of cyclic AMP and corticosterone. It is estimated that cyclic AMP production need proceed at less than 20% of maximum to induce maximum corticosterone production. ACTH_1–24, [Lys¹⁷, Lys¹⁸]ACTH_1–8 amide, and ACTH_1–16 amide induce a maximum rate of cyclic AMP and of corticosterone production equal to those of ACTH_1–39. The relative potencies as determined by cyclic AMP and by corticosterone production are in excellent agreement. The analog, ACTH_5–24, induces maximum cyclic AMP production equal to 45% of that of the natural hormone, but as predicted, induces maximum corticosterone production equal to that of ACTH_1–39. The derivative, [Trp(Nps)⁹]ACTH_1–39 induces 77% of maximum corticosterone production and less than 1% of maximum cyclic AMP production. The fragment ACTH_11–24 is a competitive antagonist of ACTH_1–39 for both cyclic AMP and corticosterone production. The observations on agonists, a partial agonist and a competitive antagonist are in harmony with the “second messenger” role assigned to cyclic AMP. A provisional model, based on the fit of the experimental observations to a set of equations, provides expressions of “intrinsic activity,” “receptor reserve”, “sensitivity”, and “amplification” in terms of maximum cyclic AMP production, concentration of ACTH which induces $\text{1}\text{2}$ maximum cyclic AMP production and concentration of cyclic AMP which induces $\text{1}\text{2}$ maximum corticosterone production.     

Effects of hypophysectomy, adrenalectomy and corticosterone treatment on uptake and release of putative central neurotransmitters by rat hypothalamic tissue in vitro.

Uptake and release of radiolabeled serotonin, noradrenaline, dopamine, acetylcholine and GABA by rat hypothalamic tissue $\text{in virto}$ were examined following various treatments, which cause drastic changes in the tissue levels of corticosterone. Hypophysectomy affected both uptake and release of most of the neurotransmitters studied. However, adrenalectomy had a more selective effect, changing these processes for serotonin only. The uptake of radiolabeled serotonin by synaptosomes was decreased by about 30%, while its release from tissue slices upon depolarization with 40 mM K⁺ was increased 25%. Both of these changes could be prevented by injecting adrenalectomized rats with corticosterone.It is suggested that corticosteroid hormones might play a modulatory role in maintaining a certain functional activity level in central serotonergic neurons.     

Somatocrinin,growth hormone releasing factor,stimulates secretion of growth hormone in anesthetized rats

The synthetic replicate of a 44 amino acid peptide isolated from a human pancreatic tumor which had caused acromegaly possesses high specific activity to release growth hormone (GH) in anesthetized male rats. The GH secretion induced by this peptide is dose-dependent from 50 ng to 1 μg, with plasma GH concentrations increasing more than 10-fold within 5 min of iv administration at the higher doses. Two enzymatic degradation products of the 44 residue peptide were also isolated and consist of the first 37 and 40 amino acids. All three peptides appear to possess similar potency, on a molar basis, $\text{in}\text{vivo}$, contrary to $\text{in}\text{vitro}$ results. The specificity of these peptides on GH release was shown by their failure to alter plasma concentrations of prolactin (PRL), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and corticosterone. Based on these $\text{in}\text{vivo}$ results, the three peptides with serve as powerful tools with which to investigate the mechanisms of GH secretion.     

L-histidine induced changes in adenosine 3':5'-monophosphate levels in rat brain and amounts of apo-, holo-a and holo-b fatty acid synthetases in rat liver.

When fasted rats were fed a chow or fat-free diet supplemented 5% with L-histidine for three days, the brain adenosine 3′:5′-monophosphate (cAMP) level increased. A 50% increase occurred in rats fed a chow diet and 20% increase in rats fed a fat-free diet. Purification of liver fatty acid synthetase and the isolation of liver apo-, holo-$\text{a}$ and holo-$\text{b}$ fatty acid synthetases demonstrated that L-histidine feeding caused changes in the relative amounts of these enzymes. Apo- and holo-$\text{b}$ fatty acid synthetases increased while the holo-$\text{a}$ form simultaneously decreased. This effect was observed in rats fed either chow or fat-free diets supplemented with L-histidine.     

Liver microsomal DT diaphorase: noninvolvement in hydroxylation of benzo(a)pyrene.

A highly purified reconstituted system isolated from the microsomes of 3-methylcholanthrene-treated rats consisting of cytochrome P-448, NADPH-cytochrome $\text{c}$ reductase and synthetic dilauroyl phosphatidylcholine had no DT diaphorase activity, but hydroxylated benzo[a]pyrene at a faster rate than microsomes from 3-methylcholanthrene-treated rats. DT diaphorase purified from liver microsomes of 3-methylcholanthrene-treated rats when added to this reconstituted system did not stimulate or inhibit benzo[a]pyrene hydroxylation, nor could it replace or NADPH-cytochrome $\text{c}$ reductase in supporting the reaction. We therefore conclude that microsomal DT diaphorase is not involved in microsomal hydroxylation of benzo[a]pyrene to its phenolic products despite the observation that both DT diaphorase activity and the hydroxylation of benzo[a]pyrene are induced by 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-$\text{p}$-dioxin     

Decreased liver cytosol glucocorticoid receptors in protein-deficient rats

A low protein diet (5% as compared to a control 21% protein diet, $\text{ad libitum}$) caused a significant decrease in the concentration of liver cytoplasmic glucocorticoid receptors; the equilibrium dissociation constant (Kd) did not change. The maximum decrease occurred in two weeks and was reversible upon substitution of the low protein by a control diet. This influence of protein deficiency could not be attributed to elevated plasma corticosterone levels since a comparable increase in plasma corticosterone of calorie-deficient rats (21% protein diet in restricted quantity) did not decrease glucocorticoid receptors and the difference in receptor levels of control and protein deficient animals persisted following adrenalectomy. These results suggest that glucocorticoids might not exert their usual biologic effects in the presence of protein malnutrition.     

In vivo lipogenesis and enzyme levels in adipose and liver tissues from pair-fed genetically obese and lean rats

Genetically obese Zucker rats pair-fed to lean controls were similar in body weight and food intake, however, epididymal fat pads were considerably larger than lean controls. $\text{In}$$\text{vivo}$ incorporation of acetate-¹⁴C into adipose tissue lipid was not significantly different, however, $\text{in}$$\text{vivo}$ liver lipogenesis was elevated in the obese rat. Characterization of enzyme profiles in both liver and adipose tissues revealed that enzymes normally associated with lipogenesis were elevated in liver tissue from obese rats. Malic enzyme and citrate cleavage enzyme were both depressed in adipose tissue of obese animals. From these data, it appears that the liver may be prominently involved in the development of excessive blood lipid and enlarged fat cells in the Zucker obese rat.     

Involvement of the neurointermediate lobe of the pituitary gland in the secretion of prolactin and luteinizing hormone in the rat

The relationship between prolactin (PRL) secretion and the neurointermediate lobe (NIL) of the pituitary gland was investigated. Plasma PRL concentrations in rats bearing anterior pituitaries autografted with or without the NIL to the renal capsule were elevated to equal extents at 1 through 6 weeks after surgery (p > 0.10). PRL levels in ovariectomized rats in which the NIL had been removed surgically (NIL-X) or only visualized (NIL-C) were 3–7 ng/ml 4, 7, and 28 days after surgery (p > 0.10); however, they were slightly higher in NIL-X $\text{vs.}$ NIL-C rats 14 days after surgery (p < 0.05). Plasma luteinizing hormone (LH) concentrations in NIL-C rats increased by 36% from 2 to 4 weeks after surgery (p < 0.05); this increase was not detected in NIL-X rats. PRL and LH surges were induced by estradiol implants in ovariectomized NIL-X and NIL-C rats; the profiles of the PRL surges were superimposable, although the magnitude of the LH surge was only 50% that in NIL-C rats (p < 0.05). These results cast doubt on the importance of the NIL in the regulation of PRL secretion either $\text{via}$ secreting hypophysiotropic hormones or $\text{via}$ conducting anterior pituitary hormones directly to the median eminence. However, the NIL may have a physiologically important role in the regulation of LH secretion.     

A method for the isolation of lipid droplet fractions from decapsulated rat adrenals

Ultrastructural and cell fractionation studies implicate lipid droplets in the storage of cholesterol and in the secretion of steroids. To evaluate the role of the lipid droplet in steroidogenesis, a discontinuous gradient centrifugation method has been developed for the isolation of both lipid droplet and non-lipid fractions from decapsulated rat adrenal homogenates. Steroids were extracted from the fractions with chloroform/methanol; the cholesterol ester, cholesterol and corticosterone in each extract were purified using a single chromatogram and the purified steroid and sterols were assayed fluorometrically. The lipid droplet fraction contained 85% of the esterified cholesterol and 32% of the free cholesterol found in whole gland extracts. Although adrenal lipid droplet fractions isolated from non-stimulated control animals contained 65–79% of the total corticosterone assayed in extracts of the whole gland, $\text{in vivo}$ injections of ACTH did not increase corticosterone 1n this fraction. On the other hand, the corticosterone measured in non-lipid fraction extracts increased significantly following ACTH treatment. These results suggest that the synthesis/release mechanism for corticosterone is not associated with the lipid droplets but may involve specific components in the non-lipid fraction. The function of lipid droplet corticosterone is unknown.     

Dopamine and norepinephrine stimulate somatostatin release by median eminence fragments invitro

The effect of catecholamines on somatostatin release by median eminence (ME) fragments was evaluated using an $\text{in}$$\text{vitro}$ incubation system. Adult male rats were used as tissue donors. Somatostatin release was readily detected during short-term incubations (10 and 30 minutes). Dopamine (DA) significantly stimulated somatostatin release during a 30 minute incubation period at the two doses tested (0.6 and 6 μM). Under similar conditions, norepinephrine (NE) stimulated somatostatin release only at the 6 μM dose. Using a shorter incubation period (10 min) and a 6 μM dose, only DA stimulated somatostatin release. The effects of DA and NE were specifically blocked by the $\text{in}$$\text{vitro}$ addition of pimozide or phentolamine, respectively, suggesting that dopaminergic and noradrenergic receptors may be present in the somatostatinergic terminals of the ME. The results indicate that both DA and NE may be involved in the regulation of somatostatin secretion.     

Location and characterization of opiate receptors regulating pituitary secretion

The site at which opiate agonists and antagonists act to alter secretion of prolactin, growth hormone and luteinizing hormone as well as the pharmacological specificity of the opiate receptors mediating these effects were examined in rats. Injection of β-endorphin but not a 10 fold higher dose of the non opiate peptide β-endorphin, increased release of prolactin and growth hormone in male rats while inhibiting luteinizing hormone release in ovariectomized, estrogen primed female rats. Prior treatment with naltrexone i.p. blocked these responses. Injection of naltrexone into the hypothalamus lowered prolactin release. In rats with a surgically formed hypothalamic island systemic administration of morphine or naltrexone altered prolactin release in the same manner as was observed in intact animals. In contrast no effects of β-endorphin or naltrexone were observed on the spontaneous secretion of prolactin $\text{in}$$\text{vitro}$. In addition β-endorphin did not alter the inhibition of prolactin release produced by apomorphine $\text{in}$$\text{vitro}$. The ED₅₀ for stimulation of prolactin release following intraventricular administration of β-endorphin or the synthetic enkephalin analog FK 33-824 was the same, approximately 0.1 ng/rat. However FK 33-824 at 0.2 ng/rat was able to produce much greater analgesia and catatonia than β-endorphin. The metabolism and distribution of β-endorphin was examined but did not account for these differential effects. These results indicate that opiate agonists and antagonists can act at the hypothalamic but not the anterior pituitary level to alter release of prolactin, growth hormone and luteinizing hormone. In addition the data suggest that the opiate receptors mediating release of prolactin may have a different pharmacological specificity from those involved with analgesia and catatonia.     

Increased somatostatin release from pancreases of alloxan diabetic rats perfused in vitro.

Insulin, glucagon, and somatostatin release $\text{in vitro}$ from perfused pancreases of normal and alloxan-diabetic rats were compared. Insulin and glucagon responses to arginine were decreased in the diabetic group whereas both basal and arginine-stimulated somatostatin release was increased. These results suggest that alterations in pancreatic D cell $\text{function}$ as well as in D cell $\text{mass}$ may contribute to the abnormal insulin and glucagon secretion found in alloxan diabetes.