Streptozotocin-induced experimental diabetes causes a time-dependent inhibition of growth and steroidogenic capacity of rat adrenal zona glomerulosa

The effects of streptozotocin-induced experimental diabetes on the morphology and secretory activity of the zona glomerulosa were studied in rats whose hypothalamo-hypophyseal-adrenal axes and renin-angiotensin systems had been pharmacologically interrupted by the simultaneous administration of dexamethasone-captopril and maintenance doses of ACTH-angiotensin II. The animals were examined 7, 14, 21, and 28 days after diabetes induction, which was evidenced by conspicuous hyperglycemia. Experimental diabetes caused notable atrophy of the zona glomerulosa and its cells, along with a significant decrease in both basal and angiotensin II-stimulated plasma aldosterone concentration. There was a positive linear correlation between all these changes and the number of days elapsed after streptozotocin administration. These data indicate that experimental diabetes exerts a profound time-dependent direct inhibition of rat zona glomerulosa. The hypothesis is advanced that the chronic lack of insulin that occurs in rats treated with streptozotocin, may depress de novo synthesis of structural and enzymatic proteins in zona glomerulosa cells and reduce their growth and steroidogenic machinery.     

Effects of chronic administration of a methionine-enkephalin analogue on the zona glomerulosa of the rat adrenal cortex

The effects of D-ala2-met-enkephalinamide (DALA) on the zona glomerulosa of dexamethasone-ACTH-treated rats were investigated by coupled radioimmunologic and morphometric techniques. Short-term DALA administration provoked a significant increase in the aldosterone plasma level along with a notable lipid droplet depletion in zona glomerulosa cells. Long-term DALA treatment induced a striking hypertrophy of zona glomerulosa cells and a further rise in the blood concentration of aldosterone. These findings seem to indicate that DALA is involved not only in the acute enhancement of aldosterone output but also in the stimulation of the growth and steroidogenic capacity of rat adrenal zona glomerulosa.     

Sensitization to repeated morphine injection in the rat: possible involvement of A10 dopamine neurons

Daily administration of morphine in rats produces an increase in the motor stimulant effect of subsequent morphine injections. This study was designed to characterize the behavioral sensitization produced by daily morphine and to evaluate the involvement of the mesolimbic and/or mesocortical dopamine (DA) neurons. Daily injection of morphine for 7 days produced an increase in both horizontal and vertical photocell counts. There was no difference in morphine levels in the blood or brain between daily morphine- and daily saline-treated rats at 30 or 90 min after acute injection of morphine. The increase was present for 60 days after initiating treatment and was associated with increases in locomotion, rearing, sniffing, grooming and bursting. Sensitization to morphine was prevented by pretreatment with naloxone i.p. or naltrexone methobromide injection into the ventral tegmental area (VTA; location of A10 DA perikarya projecting to limbic and cortical areas). In contrast, pretreatment with the same dose of naltrexone methobromide injected into the nucleus accumbens (limbic DA terminal field) or lateral ventricles did not significantly attenuate behavioral sensitization to morphine. Daily intra-VTA injections of the mu opioid agonist Tyr-D-Ala-Gly-NMe-Phe-Gly-ol enhanced the behavioral stimulant effect of acute morphine. The effects of daily morphine treatment on DA systems were evaluated by measuring DA metabolism, dopa accumulation and DA depletion in the VTA and various DA terminal fields including the prefrontal cortex, nucleus accumbens and striatum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of metaphit on dopaminergic neurotransmission in rat striatal slices: involvement of the dopamine transporter and voltage-dependent sodium channel.

Metaphit, an isothiocyanate analog of phencyclidine (PCP), increased the basal release of radioactivity (outflow) from perfused rat striatal slices preloaded with [3H]dopamine above levels observed with the dopamine uptake blocker nomifensin. Preperfusing the slices with metaphit, followed by its removal, attenuated the amphetamine- or dopamine-induced outflow. In slices prepared from reserpine-pretreated rats, the metaphit (100 microM)-induced outflow was reduced to that observed with 10 microM nomifensin, suggesting a vesicular releasing effect of metaphit in addition to dopamine uptake blockade. Electrically induced overflow of radioactivity from normal slices was stimulated by nomifensin and PCP, and by metaphit at 3 microM; it was unaffected by metaphit at 10 and 25 microM, and inhibited by higher concentrations of metaphit. Evidence that the latter effect is due to blockade of voltage-dependent sodium channels is as follows. First, metaphit, as did PCP, inhibited the binding of [3H]batrachotoxinin A 20-alpha benzoate to rat striatal synaptoneurosomes by increasing its dissociation rate; the effect of PCP, but not that of metaphit, was reversible by washing. Second, metaphit, as did PCP, inhibited veratridine (5 microM)-induced influx of [14C]guanidinium ion into synaptoneurosomes. Third, metaphit inhibited overflow of radioactivity from [3H]dopamine-preloaded slices induced by 2.5 microM veratridine, as did the sodium channel blocker tetrodotoxin.     

Chemical oxidant potentiates electrically and acetylcholine-induced contraction in rat trachea: possible involvement of cholinesterase inhibition

To determine the roles of oxidants in airway responsiveness, we studied the effects of the chemical oxidant N-chlorosuccinimide (NCS) on the contractile responses to electrical field stimulation (EFS) and acetylcholine (ACh) in isolated rat tracheal smooth muscle segments. Effects of NCS on the contractile response to EFS (5 Hz, 20 sec of duration, 50 V) reached the maximum with a 60-min incubation time. NCS potentiated the contractile response to EFS, with a maximum effect at 3 x 10(-7) M and to ACh, with a maximum effect at 3 x 10(-6) M. Thus, at a concentration of 3 x 10(-6) M, NCS significantly decreased log ED50 concentration of ACh from a control value of -5.56 +/- 0.05 to -6.24 +/- 0.06. Physostigmine (10(-7) M), at a concentration that did not alter resting tension, mimicked NCS-induced effects on contractile responses to ACh and EFS with the greater degree of shift in the respective dose-response curves. However, NCS failed to alter dose-response curves to carbachol. Removal of the epithelium shifted the dose-response curves to ACh to lower concentrations, but NCS showed similar effects on dose-response curves to ACh with and without the epithelium. Active staining showed that both acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) activities were found in the smooth muscle of the rat trachea. NCS inhibited both enzyme activities from rat tracheal homogenates in a concentration-dependent fashion. These results suggest that NCS potentiates cholinergically induced contraction by decreasing cholinesterase activity and that the oxidation of cholinesterase may cause hyperresponsiveness of airway smooth muscle by inhibition of the enzyme activity.     

Effects of prolonged dopamine infusion on the zona glomerulosa of sodium-restricted rats treated or not with prolactin: Stereology and plasma hormone concentrations

Prolonged sodium restriction was found to induce a notable hypertrophy of rat zona glomerulosa (ZG) cells and a significant rise in the basal plasma aldosterone concentration. Chronic prolactin administration significantly furthered the effects of sodium restriction. Dopamine infusion (3 mg/kg day for 7 days) did not apparently affect ZG morphology and function in the control rats, while it significantly counteracted the effects of sodium deprivation combined or not with prolactin administration. However, the action of dopamine was less intense in sodium-deprived rats treated with prolactin. These findings confirm the view that the dopaminergic system exerts a tonic inhibitory effect, modulated by the sodium balance, on the growth and secretory activity or rat ZG. Moreover, they suggest that the mechanism(s) underlying the antiadrenoglomerulotrophic action of dopamine in rats only partially involve(s) the well-known suppression of the hypophyseal release of prolactin.     

Effects of beta-phenylethylamine on dopaminergic neurons of the ventral tegmental area in the rat: a combined electrophysiological and microdialysis study

The effects of systemic administration of beta-phenylethylamine (beta-PEA) and microiontophoretically applied beta-PEA on the spontaneous discharge of dopamine (DA) neurons in the ventral tegmental area (VTA) of the anesthetized rat were examined. Intravenous administration of beta-PEA (1.0, 2.5, and 5.0 mg/kg) and microiontophoretic applications of beta-PEA caused inhibitory responses in DA neurons. Systemic administration and microiontophoretic applications of beta-PEA induced dose- or current-dependent responses. The systemic beta-PEA-induced inhibitory responses were reversed by pretreatment with the DA D(2) receptor antagonists haloperidol (0.5 mg/kg i.p.) and sulpiride (10 mg/kg i.p). Pretreatment with reserpine (5 mg/kg i.p. 24 h earlier) did not completely block the systemic administration of beta-PEA (2.5 mg/kg) inhibition. A microdialysis study of freely moving rats demonstrated that the extracellular DA level increased significantly in response to local application of beta-PEA (100 muM) in the VTA via a microdialysis probe, and local application of beta-PEA-stimulated somatodendritic DA release in the VTA. The beta-PEA-induced release of DA was calcium ion-independent and was enhanced by pretreatment with pertussis toxin. These findings indicate that beta-phenylethylamine inhibits DA neuron activity via DA D(2) autoreceptors in the rat VTA and that this inhibitory effect is mediated by the somatodendritic DA release.     

Effects of neuromedin U-8 on the secretory activity of the rat adrenal cortex: evidence for an indirect action requiring the presence of the zona medullaris

The acute effect of increasing concentrations (from 10^?8 to 10^?6 M) of neuromedin U-8 (NMU-8) on steroid secretion of rat adrenal gland was investigated in vitro by high-pressure liquid chromatography. The production of the following steroids was measured: pregnenolone (PREG), progesterone (PROG), 11-deoxycorticosterone (DOC), corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18OH-DOC), 18-hydroxycorticosterone (18OH-B) and aldosterone (ALDO). NMU-8 had no effects on either dispersed adrenocortical cells or fragments of adrenocortical autotransplants lacking medullary chromaffin cells. Conversely, NMU-8 exerted concentration-dependent secretagogue effects on adrenal slices, including both cortex and medulla. At all concentrations tested, NMU-8 increased the production of both PREG and total post-PREG steroids. The increase in total post-PREG steroid output induced by low concentrations of NMU-8 (10^?8 M) was due to similar rises in the production of non-18-hydroxylated steroids (PROG, DOC and B) and 18-hydroxylated hormones (18OH-DOC, 18OH-B and ALDO); conversely, that provoked by higher concentrations of the neuropeptide (10^?7 to 10^?6 M) was almost exclusively caused by the rise in the yield of 18-hydroxylated steroids. The stimulating effect of NMU-8 on PREG output was blocked by both α-helical-CRH and corticotropin-inhibiting peptide, which are competitive inhibitors of CRH and ACTH, respectively. The following conclusions have been drawn: (1) NMU-8 affects adrenal steroid secretion indirectly by acting on the medullary chromaffin cells, which in turn may paracrinally stimulate the cortical ones; (2) at all concentrations tested, NMU-8, by stimulating the intramedullary CRH/ACTH system, causes a net rise in the activity of the early ratelimiting step of steroidogenesis, with the consequent increase in the output of the entire spectrum of post-PREG steroids; and (3) at higher concentrations (over 10^?8 M), NMU-8 also elicits the release from chromaffin cells of a factor (not yet known) that specifically enhances 18-hydroxylase activity.     

Dopamine analog-induced hyperglycemia in rats: involvement of the adrenal medulla and the endocrine pancreas

The following synthetic, structural analogs of dopamine (DA) were examined for their ability to produce hyperglycemia in conscious unrestrained rats: APO (apomorphine), RDS-127 (2-di-n-propylamino-4,7-dimethoxyindane), di-n-propyldopamine, 2-di-n-propylamino-5,6-dihydroxytetralin, 2-dimethylamino-6,7-dihydroxytetralin, lergotrile, pergolide, bromocriptine and d-amphetamine. All the compounds demonstrated dose- and time-dependent hyperglycemic actions. The most potent DA analog to induce hyperglycemia was 2-di-n-propylamino-5,6-dihydroxytetralin (0.18 mumol/kg) and, at the doses used, 2-dimethylamino-6,7-dihydroxytetralin produced the greatest elevation in blood glucose (227% control). APO and RDS-127 were used in experiments designed to provide additional mechanistic information concerning their hyperglycemic action. The hyperglycemia produced by APO or RDS-127 was blocked by adrenalectomy, adrenodemedullation or prior administration of pimozide, a DA receptor antagonist. Phentolamine, an alpha adrenergic receptor antagonist had no effect on the hyperglycemia induced by APO or RDS-127. Oral glucose tolerance tests indicated that APO and RDS-127 caused abnormal glucose tolerance and inhibited the compensatory increase in serum immunoreactive insulin. These effects were prevented by pimozide or phentolamine pretreatment. The potencies of the compounds to produce increases in serum glucose concentrations (SG), inhibit the accumulation of DOPA using the in vivo gamma-butyrolactone procedure (DOPA) and inhibit food intake (FI) were subjected to correlation analysis. Positive correlations were found for FI vs. DOPA, r = 0.96; SG vs. decreases DOPA, r = 0.98 and SG vs. FI, r = 0.98.(ABSTRACT TRUNCATED AT 250 WORDS)     

A possible involvement of the central endorphin system in the autoanalgesia induced by chronic administration of Freund's adjuvant solution in rats

Chronic pain was induced in rats by daily injections of complete Freund's adjuvant into hind paws. Daily changes of pain threshold and endorphin (ED) content and their receptors in 4 divided parts: cortex, diencephalon-mesencephalon containing striatum (D-M), pons-medulla (P-M) and spinal cord, were measured. Decrease in pain responsiveness was observed in the adjuvant-injected group with concomitant increase of ED content in P-M and spinal cord. This decrease in pain responsiveness in the adjuvant-injected group was significantly different from that in the non-treated control group being partially reversed by naloxone. Furthermore, [3H]met-enkephalin binding sites increase in number in P-M of the adjuvant-injected group when maximal decrease of pain responsiveness was observed, returning to control level thereafter. Scatchard analysis revealed the increase of the low affinity binding site in P-M of the adjuvant-injected group. In cortex and D-M, on the other hand, ED content tended to decrease and no change was observed in number of [3H]met-enkephalin binding sites. These results indicate that the ED system in P-M and spinal cord may be more substantially involved in autoanalgesia than in cortex and D-M.     

Effects of a single dose of methamphetamine and iprindole on the serotonergic and dopaminergic system of the rat brain

A single dose (17.5 mg/kg i.p.) of methamphetamine was administered to iprindole-treated (10 mg/kg i.p.) rats. Forebrain concentrations of methamphetamine and amphetamine were significantly increased in iprindole-treated rats 1 and 6 hr after injection; in contrast to rats pretreated with saline, both amines were also detected after 18 hr. Three and 7 days after injection, significant decreases were seen in tryptophan hydroxylase (TPH) activity and serotonin concentrations in the cerebral cortex, neostriatum and hypothalamus. Hypothalamic TPH activity had recovered by 14 days. Neostriatal tyrosine hydroxylase activity and dopamine concentrations were significantly depressed at all time points examined. Iprindole alone produced a significant increase in cortical TPH activity after 1 day. After 3 days, TPH activity was significantly decreased when compared with control, whereas serotonin and 5-hydroxyindoleacetic acid concentrations were significantly increased. This study demonstrates that persistence of methamphetamine and/or amphetamine at the site of action is important for neurotoxicity.     

Effects of prenatal reserpine administration on development of the rat adrenal medulla and central nervous system.

Reserpine (1 mg/kg s.c.) was administered to pregnant rats at different periods of gestation. Rats born to mothers who received reserpine on days 6, 5 and 4 or 4, 3 and 2 before delivery showed early postnatal adrenal catecholamine depletion, an effect which can be attributed to a direct action of the drug; however, at no time was induction of tyrosine hydroxylase or dopamine beta-hydroxylase observed. Administration of reserpine on days 9, 8 and 7 before delivery did not alter postnatal adrenal catecholamine levels in the offspring but produced permanent elevations in enzyme activities and vesicular amine uptake beginning at 10 days of age. Studies utilizing direct stimulation with nicotine indicated that the inherent responsiveness of the adrenal medulla itself was the same in control and reserpine-exposed pups. These data all suggest that sympathoadrenal tone has been permanently increased in the offspring of rats which have been exposed to reserpine early in gestation. In the brain, administration of reserpine on days 6, 5 and 4 before delivery resulted in a delay in early postnatal development of brain weight and synaptosomal uptake mechanisms, and at later stages subnormal tyrosine hydroxylase activities. When reserpine was given on days 9, 8 and 7 before delivery, only the deficiency in tyrosine hydroxylase was seen. These studies indicate that long-lasting changes in both peripheral and central nervous system catecholamine disposition can be produced by prenatal reserpine administration.     

Effects of galanin on the secretory activity of the rat adrenal cortex: in vivo and in vitro studies

Galanin, a 28-amino-acid peptide originally isolated from pig intestine, was found to cause dose-dependent rises in the plasma concentration of corticosterone in hypophysectomized rats and in both basal and submaximally ACTH-stimulated in vitro corticosterone production by adrenal quarters and isolated zona fasciculata/reticularis cells. These findings indicate that galanin exerts a direct glucocorticoid secretagogue effect on the inner adrenocortical zones and suggest that galanin, high concentrations of which are contained in adrenal chromaffin cells, may be included in that group of regulatory peptides, by way of which adrenal zona medullaris is thought to exert a paracrine control on the function of the zona corticalis. Galanin was also found to increase the plasma level of aldosterone in hypophysectomized rats in a dose-dependent manner without inducing changes in natremia, kalemia, plasma renin activity, or ACTH plasma concentration. Galanin did enhance both basal aldosterone output and that following submaximal ACTH or angiotesin II stimulation aldosterone out-put from adrenal quarters, but not from isolated zona glomerulosa cells. This last, rather unexpected, result suggests that galanin exerts an indirect mineralocorticoid secretagogue action, which seems to require the structural integrity of the adrenal cortex and the presence of the adrenal medulla. The hypothesis is advanced that galanin may control the release of some medullary peptides, which in turn may affect mineralocorticoid secretion of the zona glomerulosa in a paracrine manner.     

Effects of oxytocin on the function and morphology of the rat adrenal cortex: in vitro and in vivo investigations

The effects of oxytocin (OX) on the function and morphology of the rat adrenal cortex were studied in vivo and in vitro. OX exerted a potent stimulatory action on basal, but not 10⁻⁸ M ACTH-stimulated corticosterone (B) secretion of dispersed rat inner (zona fasciculata and zona reticularis) adrenocortical cells (maximal effective concentration: 10⁻⁹ M); in contrast, at higher concentrations (10⁻⁷/10⁻⁶ M) OX inhibited maximally ACTH-stimulated B output. A single subcutaneous (s.c.) injection of 1.2 nmol/100 g body weight OX resulted in a longlasting (up to 12 h) rise in plasma B concentration (PBC). The prolonged administration of OX (daily s.c. injections of 0.6 or 1.2 nmol/100 g for 10 days) caused a marked lowering in the adrenal weight and volume of all adrenocortical zones, that in turn was due to a decrease in the number of their parenchymal cells; however, the average volume of inner adrenocortical cells was significantly increased. Basal PBC was lowered, but its response to ether stress was unchanged in comparison with control rats. Prolonged OX treatment did not change B secretion by adrenal slices, but it markedly raised that of dispersed inner adrenocortical cells. Our present findings clearly show that the effects of OX on the adrenal cortex depend on the experimental model employed (in vitro versus in vivo) and the duration of treatment (acute versus chronic). Taken together they allow us to conclude that OX exerts an acute direct stimulatory effect on the rat adrenal cortex, and a chronic inhibitory one, that at least in part could be due to the interference of OX with the mechanism(s) of intracellular transduction of the ACTH secretagogue signal.     

Obstructive nephropathy in the rat: possible roles for the renin-angiotensin system, prostaglandins, and thromboxanes in postobstructive renal function.

Relief of unilateral ureteral obstruction (UUO) of 24 h duration in rats is followed by severe renal vasoconstriction in the postobstructive kidney (POK). The present study examined possible roles of renal prostaglandins (PG) and thromboxanes (TX), as well as the renin-angiotensin system, in this vasoconstriction. Administration of the cyclooxygenase inhibitor indomethacin, which blocks both PG and TX production, failed to improve POK hemodynamics in UUO rats. To explore the possible role of the TX compounds, which include the potent vasoconstrictor thromboxane A2 (TXA2), UUO rats were infused with imidazole, an agent that blocks synthesis of TX, but not of PG. Imidiazole led to two- to threefold increases in the clearance of both inulin and rho-aminohippuric acid by the POK. This effect of imidazole was abolished by indomethacin, suggesting that the amelioration of POK vasoconstriction by imidazole was a result of inhibition of vasoconstrictor TX synthesis (e.g. TXA2), with PG vasodilators (e.g. PGE2 or PG12) still active. Urea, infused in a solution whose osmolality and volume were identical to the imidazole infusion, failed to improve hemodynamics in the POK, making it unlikely that nonspecific effects of volume expansion or osmotic diuresis mediated the beneficial effect of imidazole. Further studies examined the possible role of the renin-angiotensin systems in the vasoconstriction of the POK. UUO rats infused with the angiotensin II antagonist, Saralasin, exhibited no significant improvement in POK function, a finding that might be at least partly attributable to agonist/vasoconstrictor properties of Saralasin. In other experiments, treatment of UUO rats with the angiotensin-converting enzyme blocker SQ 14225 (Captopril), in order to inhibit angiotensin II formation, led to at least twofold increases in the clearance of both inulin and rho-aminohippuric acid in the POK. It is unlikely that Captopril exerted this beneficial effect by potentiating the vasodilator kinins, because the effect was not diminished by administration of either carboxypeptidase B (which destroys the kinins) or Trasylol (which blocks kinin synthesis). Thus, these results suggest that both angiotensin II, as well as metabolites of the PG-TX system, may be important determinants of postobstructive renal hemodynamics in the rat.     

A biochemical and morphologic study of myelination and demyelination. II. Lipogenesis in vitro by rat nerves following transection

Bilateral transection was performed on rat sciatics. At varying intervals after the operation, samples of nerve were taken both distal and proximal to the level of transection, as well as from the tissue which bridged the gap between the stumps. These samples were incubated in Warburg flasks, with glucose and a labelled lipide precursor (acetate or phosphate). The total lipides were then extracted and their radioactivity was measured. Normal rat sciatics served as controls, and the biochemical and histological findings were correlated. In the distal portion undergoing Wallerian degeneration, the lipide content began to fall before any removal of myelin could be detected histologically. It is suggested that there is a period of "non-cellular removal" prior to the physical breakdown of the myelin. Changes in respiration and in lipogenesis from acetate followed a triphasic course, and agreed with the histological findings in that after a period of predominantly passive changes (approximately 1 to 3 days) there follows a period of cellular reaction (4 to 50 days) and a period of atrophy (from 50 days onward). The incorporation of phosphate into the lipides was increased at all stages examined, even as early as 22 hours after section. This increased P³² incorporation could not be reproduced in nerves allowed to degenerate in vitro. It is suggested that the hypertrophying Schwann cells synthesize some lipide moieties at a considerably faster rate than others. Proximal to the level of transection, lipogenesis from acetate was depressed, for as long as 32 days postoperatively. It appears, therefore, that the maintenance of the myelin sheath is impaired also above the level of transection. In the "union tissue" which developed between the stumps, prior to the appearance of histologically visible myelin, lipogenesis was low; later it rose above levels for normal nerve. This pattern of lipogenesis in regenerating nerve is similar to that found in growing nerves.