Investigations on the possible involvement of the dopaminergic system in the modulation of the growth and steroidogenic capacity of the rat adrenal zona glomerulosa: A coupled morphometric and biochemical study

Abstract

The effects of metoclopramide (MTC) and bromocriptine (BRC) (two drugs which act as antagonist and agonist of DOPA-receptors, respectively) on the zona glomerulosa of dexamethasone/ACTH-treated rats were investigated by coupled biochemical and morphometric techniques. Short-term (1-h) MTC administration significantly increased the plasma concentration of aldosterone, while long-term (7-day) MTC administration, as well as short- and long-term treatment with BRC did not cause any apparent change. Long-term MTC administration was found to significantly potentiate both the rise in the plasma level of aldosterone and the hypertrophy of the zona glomerulosa and its parenchymal cells induced by a prolonged treatment with angiotensin II (AII), but not those evoked by a chronic sodium deprivation alone or combined with AII infusion. Long-term BRC administration notably counteracted the effects of sodium restriction (coupled or not with AII infusion), but not those induced by the administration of AII alone. Long-term MTC administration partially reversed both the lowering of the plasma concentration of aldosterone and the atrophy of the zona glomerulosa and its parenchymal cells caused by a prolonged sodium-loading (combined or not with captopril infusion), but not those produced by the administration of captopril alone. On the other hand, long-term BRC treatment induced a further significant reduction in the blood level of aldosterone and the volume of zona glomerulosa and its cells only in captopril-treated animals. These findings are consistent with the view that the dopaminergic system exerts a maximal tonic inhibitory effect not only on the secretory activity, but also on the growth and steroidogenic capacity of the rat zona glomerulosa. Furthermore, they suggest that the activity of the dopaminergic system is in turn controlled by the sodium balance, being almost completely suppressed by a prolonged sodium deprivation.

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

“…Our results also confirm the contention that an increase in angiotensin II production is not the sole mechanism whereby prolonged sodium deprivation stimulates the growth of rat ZG [15]. In fact, we used animals in which the renin-angiotensin system had been pharmacologically interrupted by captopril, an inhibitor of the angiotensin-converting enzyme [19].…”

“…In fact, we used animals in which the renin-angiotensin system had been pharmacologically interrupted by captopril, an inhibitor of the angiotensin-converting enzyme [19]. We previously suggested that the suppression of the dopaminergic system may be involved in the enhancement of the growth and secretory capacity of the ZG of sodium-restricted rats [15]. The present data indicating that dopamine infusion completely reverses the effects of sodium restriction on the ZG strengthen this hypothesis.…”

“…However, the action of dopamine was less intense in sodium-deprived rats treated with prolactin. These findings confirm the view [15] 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.…”

“…Recently, we have shown that the dopaminergic system plays also a notable role in the control of the growth of rat ZG, and that this action of dopamine is independent of any blockade of the renin-angiotensin system and ACTH release, as well as of any change in the blood level of potassium [15]. However, our findings did not rule out the possibility that the dopaminergic system may affect rat ZG indirectly by suppressing other adrenoglomerulotrophic factors, among which the main candidate appears to be prolactin.…”

Peptide growth factors and the adrenal cortex

“…Restriction of dietary sodium intake causes hypertrophy of the zona glomerulosa and its parenchymal cells, which is reflected in an increased capacity for aldosterone secretion, and elevated plasma aldosterone concentrations (Mazzocchi et al, 1987;Mü ller, 1989;Quinn and Williams, 1988;Vinson et al, 1992). These changes are at least partially mediated by the circulating RAS (Aguilera and Catt, 1978;Aguilera et al, 1978;Ganong et al, 1966;Williams and Dluhy, 1972), but additionally by a discrete glomerulosa RAS system (Mulrow, 1992;Phillips et al, 1993).…”