Influence of pinealectomy on the mitotic activity of regenerating adrenal cortex in rats

There is some evidence that the pineal gland may influence the proliferation of both normal and neoplastic cells. The adrenal cortex has very high capacity for regeneration. Therefore, the effects of pinealectomy on the mitotic activity of regenerating adrenal cortex of rats were studied on the second, seventh and twelfth days following the enucleation of adrenals. Pinealectomy caused a significant decrease in the mitotic index of regenerating adrenal cortex after 2 and 12 days in comparison to sham operated controls.     

Verapamil inhibits proliferation but not steroidogenesis of regenerating rat adrenal cortex

The effect of verapamil, a calcium channel antagonist, on proliferation and steroidogenesis was investigated in regenerating rat adrenal cortex. Verapamil was given subcutaneously in two doses (1 and 5 mg/kg) to male Wistar rats subjected to adrenal enucleation combined with contralateral adrenalectomy. It was found that verapamil inhibited the mitotic activity of adrenocortical cells on the 4th and 8th day after surgery in a dose-dependent manner. However, no changes in corticosterone secretion were observed.     

Ascorbate stimulates monooxygenase-dependent steroidogenesis in adrenal zona glomerulosa

It is well known that ascorbic acid (Asc) is highly concentrated in the adrenal gland, but its function in the gland is not thoroughly elucidated. We therefore examined the possibility that Asc participates in steroidogenic monooxygenase systems of the adrenal cortex with the aid of the regenerating system including outer mitochondrial membrane cytochrome b (OMb). When Asc availability was limited in rat mutants unable to synthesize Asc, the increase in plasma aldosterone concentration under Na-deficiency was suppressed without effect on plasma corticosterone concentration. Aldosterone formation in the isolated mitochondrial fraction of the zona glomerulosa (zG) of the adrenal cortex was stimulated by the addition of Asc and NADH, while corticosterone formation was not. Consistently zG showed a high level of Asc regeneration activity and was rich in OMb among adrenocortical zones. Taken together, the enhanced aldosterone formation that is catalyzed by one of the steroidogenic monooxygenases, P450aldo, may be supported by Asc with its regenerating system.     

Angiotensins II and IV modulate adrenocortical cell proliferation in ovariectomized rats.

Effects of angiotensins II (AngII), angiotensin IV (AngIV, 3-8 fragment of angiotensin II) and losartan (an antagonist of angiotensin receptor type 1) on the proliferation of adrenocortical cells in ovariectomized rats have been studied. The incorporation of bromodeoxyuridine (BrdU) into cell nuclei was used as an index of cell proliferation. AngIV decreased BrdU labeling index mainly in the reticularis zone and losartan (Los) was able to partially reverse this inhibitory effect of AngIV. AngII had no effect on the adrenocortical cell proliferation when given alone, however Los given simultaneously diminished BrdU incorporation into nuclei of glomerulosa and reticularis zones as compared with AngII. These findings suggest that AngII and AngIV modulate adrenocortical cell proliferation in ovariectomized rats.     

Melatonin-induced suppression of the pinealectomy-stimulated rat adrenal cortex mitotic activity

Pineal involvement in the regulation of adrenocortical mitotic activity has recently been suggested. It has been shown that melatonin (Mel) decreased the mean mitotic activity rate (MMAR) of the adrenal cortex both in vivo and in organ culture. The goal of the present study was to test the influence of pinealectomy (PX) and/or Mel-treatment on the MMAR of adrenocortical cells, as well as on the adrenal weight in rats. The stathmokinetic method was used in the study. It was found that PX significantly increased the MMAR of the adrenocortical cells. Moreover, Mel suppressed the proliferogenic effect of PX on the rat adrenocortical cells. Melatonin alone did not significantly affect the mitotic activity of the adrenal cortex. None of the three experimental procedures, i.e. Mel, PX and Mel-treatment of pinealectomized animals significantly affected the adrenal weight. The present data suggest that Mel may be involved in the inhibitory control of adrenocortical cell proliferation.     

Porcine brain natriuretic peptide, another modulator of bovine adrenocortical steroidogenesis

Porcine brain natriuretic peptide (pBNP) significantly inhibited aldosterone production stimulated by an angiotensin II analog and ACTH-stimulated cortisol secretion, together with simultaneously increasing the formation of cGMP in dispersed bovine adrenocortical cells. Receptors for pBNP were identified in bovine adrenal gland using an in vitro receptor autoradiographic technique and studies of 125I-pBNP binding. In vitro receptor autoradiography demonstrated specific binding sites for 125I-pBNP in bovine adrenal cortex. Complete displacement of 125I-pBNP by unlabeled pBNP or human atrial natriuretic peptide (hANP) can take place at these sites. Analysis of 125I-pBNP binding to bovine adrenocortical membrane fractions showed that the adrenal cortex had high-affinity, low-capacity pBNP-binding sites, with a dissociation constant (Kd) of 2.32 +/- 0.33 x 10(-10) M (mean +/- SE) and a maximal binding capacity (Bmax) of 36.7 +/- 1.6 fmol/mg protein. Moreover, the specific binding sites for 125I-pBNP were completely displaced not only by unlabeled pBNP but also by unlabeled hANP. The hANP dose required for 50% inhibition of specific 125I-pBNP binding was almost identical to that for pBNP (IC50 values for hANP and pBNP: 8.5 x 10(-10) and 6.5 x 10(-10) M, respectively). These results suggest that pBNP exerts a suppressive effect on bovine adrenocortical steroidogenesis via a receptor which may be shared with ANP.     

The involvement of angiotensins in the control of prostatic epithelial cell proliferation in the rat.

The effects of captopril (the inhibitor of the angiotensin-converting enzyme) and of angiotensins II and IV (3-8 fragment of angiotensin II) on cell proliferation of the prostatic epithelium was investigated in the rat. The incorporation of bromodeoxyuridine into cell nuclei was used as an index of cell proliferation. It was found that the treatment with captopril resulted in the suppression of prostatic epithelial cell proliferation. The antiproliferative effect of captopril was reversed (at least partially) by a simultaneous treatment with either angiotensin II or angiotensin IV. The effects of angiotensins were not blocked by the administration of losartan--AT1 angiotensin receptor blocker. These findings suggest the involvement of angiotensins in the control of prostatic growth, acting via the receptors different from the AT1-subtype (presumably via AT4 receptors).     

Effects of the hypocholesterolemic drug, 4-aminopyrazolo (3,4-d) pyrimidine (4-APP), on the hamster adrenal cortex. An ultrastructural and functional study.

The aim of this study was to gain insight into the effects of 4-aminopyrazolo(3,4-d)pyrimidine (4-APP), a hypocholesterolemic drug, on the adrenal cortex of the hamster, representing an animal species in which steroidogenesis primarily relies on utilization of cholesterol synthesized de novo in the gland. 4-APP administration (1.5 mg/animal day for 3 days) to intact or dexamethasone-suppressed hamsters resulted in a marked proliferation of adrenocortical cells. However, the volume of parenchymal cells was unchanged in intact animals and lowered in the zona glomerulosa (ZG) and zona reticularis (ZR) of dexamethasone-administered hamsters. In both groups of animals, 4-APP strikingly increased the volume of the lipid-droplet compartment and markedly reduced the surface area of smooth endoplasmic reticulum in ZF cells, without significantly affecting the volume of the mitochondrial compartment and the surface area of mitochondrial cristae. These morphologic changes displayed no evident correlation with adrenal cortisol content and secretion. Since most of the 4-APP-induced changes were not prevented by dexamethasone, it seems legitimate to suggest that they could mainly depend on a direct effect of 4-APP on the hamster adrenocortical cells.     

Ontogeny of adrenal VIP content and release from adrenocortical cells in the ovine fetus

The present study was designed to investigate the presence of VIP in fetal adrenals, to determine the changes in adrenal VIP content associated with maturation, and to explore the factors which regulate fetal adrenal VIP release. Adrenal glands from ovine fetuses at 70 to 140 days gestation were used. Adrenal VIP content, as measured by radioimmunoassay, were low at 70 and 80 days of gestation. This was followed by a rapid increase in VIP content from 80 to 110 days reaching a plateau between 110 and 130 days at levels comparable to that in the adult. A significant fall in adrenal VIP content occurred at 140 days, immediately prior to term. Release of VIP from fetal adrenocortical cells in vitro was significantly elevated by angiotensin II at 10(-5) M, while ACTH had no effect. Acetylcholine at 50 microM and high potassium stimulated fetal adrenal VIP release while norepinephrine did not. These results suggest that the VIP neuronal system in the ovine fetal adrenal matures between 80 and 110 days of gestation. Furthermore, the release of VIP from the fetal adrenocortical cells may be regulated by angiotensin II and cholinergic neurotransmitters.     

Autoradiographic distribution of 125I-VIP binding in the rat adrenal cortex

Using in vitro autoradiography, 125I-VIP binding was found to be concentrated in the capsule and glomerulosa of the rat adrenal cortex. The densest receptor distribution was coincident with the distribution of VIP nerve fibers that arborize extensively in the capsule and glomerulosa. The specificity of this binding was demonstrated using unlabelled VIP, ACTH and angiotensin II. The presence and distribution of 125I-VIP binding sites provides the link between the previously found VIP nerves and the steroidogenic effect of exogenous VIP, thereby substantiating the physiological role of VIP-containing autonomic nerves in the regulation of adrenocortical cell function.     

Influence of hormones on the functional activity of the regenerating cortex of the enucleated adrenal in situ]

The functional activity of the regenerating cortex was studied in 90 female albino rats (150-200 g) after ablation of the right adrenal and enucleation of the left one. In the period of active growth of the regenerating tissue (10 days after operation) the functional activity of parenchymatous cells was low which is evidenced by poor content of both lipids and "ketosteroids". In parallel with reparation of the adrenal adrenocortical tissue mass the content of physiologically active substances was also restored (20 days after operation). After injection of hydrocortizone (daily dosage 2,5 mg) the growth and differentiation of the bundle-reticular zone in the regenerating area was inhibited. In the glomerular zone the reactions to lipids and "ketosteroids" were mainly similar to those in the glomerular zone of intact adrenal. After injection of ACTH (daily dosage 5 or 10 mg) during 10 days the regenerating area was functionally better developed than in the control since moderately pronounced reactions to "ketosteroids" and lipids appeared in it. Fairly high content of these substances in the regenerated cortex after 20 days of injections of ACTH (10 units) as well as presence of secondary necrobiotic changes pointed to functional overstrain of the newly formed organ.     

Role of converting enzyme in the cardiovascular and adrenal cortical responses to (des-Asp1)-angiotensin I.

(Des-Asp1)-angiotensin I, angiotensin II and III were evaluated for pressor activities in conscious nephrectomized rats and for steroidogenic actions in rat adrenal zona glomerulosa. The pressor effect of this angiotensin nonapeptide was similar to that found with mole-equivalent doses of angiotensin III (one-third as active as angiotensin II) and was significantly attenuated by pretreatment with the 0. jararaca nonapeptide converting enzyme inhibitor. Hence, (des-Asp1)-angiotensin I is a substrate for converting enzyme in vivo, and the rapid conversion indicates that an alternate pathway for the formation of angiotensin III could exist. (Des-Asp1)-angiotensin I possessed only 0.1% of the activity of angiotensin III as a steroidogenic agent in cell suspensions of rat adrenal zona glomerulosa. Angiotensin I was a weak steroidogenic agent in vitro (1%) and was not blocked by an inhibitor of converting enzyme. Adrenal cells dispersed from the outer zone of the cortex would appear to be devoid of significant converting enzyme activity.     

Invalidation of TASK1 potassium channels disrupts adrenal gland zonation and mineralocorticoid homeostasis

TASK1 (KCNK3) and TASK3 (KCNK9) are two-pore domain potassium channels highly expressed in adrenal glands. TASK1/TASK3 heterodimers are believed to contribute to the background conductance whose inhibition by angiotensin II stimulates aldosterone secretion. We used task1-/- mice to analyze the role of this channel in adrenal gland function. Task1-/- exhibited severe hyperaldosteronism independent of salt intake, hypokalemia, and arterial 'low-renin' hypertension. The hyperaldosteronism was fully remediable by glucocorticoids. The aldosterone phenotype was caused by an adrenocortical zonation defect. Aldosterone synthase was absent in the outer cortex normally corresponding to the zona glomerulosa, but abundant in the reticulo-fasciculata zone. The impaired mineralocorticoid homeostasis and zonation were independent of the sex in young mice, but were restricted to females in adults. Patch-clamp experiments on adrenal cells suggest that task3 and other K+ channels compensate for the task1 absence. Adrenal zonation appears as a dynamic process that even can take place in adulthood. The striking changes in the adrenocortical architecture in task1-/- mice are the first demonstration of the causative role of a potassium channel in development/differentiation.     

Impact of angiotensin II type 2 receptor blockade on experimental radiation nephropathy

In the rat, blockade of angiotensin II type 1 receptors diminishes the functional changes that occur after kidney irradiation. It has been hypothesized that some of the beneficial effects of angiotensin II type 1 blockers in renal disease are caused by a rise in angiotensin II that stimulates the angiotensin II type 2 receptor. If this hypothesis applied in this model, blockade of the type 2 receptor should exacerbate radiation nephropathy and/or counteract the beneficial effects of type 1 receptor blockade. To assess this hypothesis, rats were given total-body irradiation plus bone marrow transplantation and then treated for 12 weeks with a type 1 receptor blocker (L158,809), a type 2 blocker (PD123319), both blockers, or no blockers. Rats were assessed for renal function (proteinuria, hypertension, azotemia) and renal failure for up to 62 weeks. Contrary to the hypothesis, the type 2 blocker alone produced a temporary delay in the development of radiation nephropathy, and it substantially enhanced the efficacy of the type 1 blocker. This implies that both type 1 and type 2 angiotensin receptors need to be blocked to achieve the maximum level of prophylaxis of radiation nephropathy. We speculate that the beneficial effect of the angiotensin II type 2 receptor blocker is due to a reduction in radiation-induced renal cell proliferation or fibrosis.