Interaction of aldosterone and oxytocin to influence renal sodium excretion in rats

Abstract

SUMMARYThe possibility of an interaction between oxytocin and aldosterone to influence renal Na+ excretion was investigated in Inactin-anaesthetized male Sprague-Dawley rats. Endogenous plasma concentrations of aldosterone were suppressed by either adrenalectomy or bicarbonate infusion. The effects of 2 h intravenous administration of oxytocin (0-04 pmol/min) and/or aldosterone (42 pmol/min) on renal Na+ handling were studied in 0077 M NaCl-infused adrenalectomized (Adx) rats and groups of intact animals that were infused with 0 077 M NaHCO3. Aldosterone alone significantly (P < 0 01) reduced Na+ excretion from pretreatment peak value of 5 0 + 1 0 to 1 5 + 0 4 flmol/min in Adx animals (n = 8) and 9 2 + 1 2 to 5 2 + 12 ,umol/min in NaHCO3-infused rats (n = 8) by 2 h after the start of administration. However, combined administration of aldosterone and oxytocin was associated with a significantly (P < 0 01) increased Na+ excretion rate from a peak pretreatment value of 68 + 07 ,tmol/min to a peak value of 11 5 ±1 ,amol/min by 1 h 40 min after the start of treatment in Adx rats (n = 7). In bicarbonate-infused rats (n = 8) Na+ excretion rose within 20 min of the start of treatment from a pretreatment peak of 9 0 + 0 8 ,tmol/min to a peak value of 13 5 + 0 8 ,tmol/min in response to combined hormone administration. In conclusion, we have shown that concomitant administration of aldosterone and oxytocin increased the rate of excretion of Na+ in two different preparations, which supports the idea of an interaction between the steroid and oxytocin to promote Na+ loss.

Relaxin-induced changes in renal sodium excretion in the anesthetized male rat

“…Oxytocin can exert a natriuretic action in the rat (10); it is required to restore renal sodium excretion after neurohypophysectomy (3) and in adrenalectomized or aldosterone-suppressed rats (28). Hence, the natriuresis observed after longterm rhRLX infusion could have been mediated, at least in part, by oxytocin.…”

Rapid natriuretic action of aldosterone in the rat

“…Ganong and Mulrow (9) observed a reduction in urinary sodium excretion in adrenalectomized dogs 5-30 min after a bolus injection of aldosterone into the aorta or renal artery. In contrast, our laboratory has previously reported that combined infusion of aldosterone and oxytocin into aldosterone-suppressed rats (adrenalectomy or sodium bicarbonate infusion) resulted in a rapid increase in urinary sodium excretion (26), contrary to the conventional, genomic antinatriuretic actions of aldosterone. Apart from these observations, little is known about the nongenomic actions of aldosterone in the intact animal.…”

“…Rats either continued to receive vehicle (2.5% dextrose, n ϭ 8) for the remaining 3 h of the experiment or received vehicle for 1 h, followed by aldosterone (42 pmol/min, Sigma-Aldrich, Poole, Dorset, UK) for 1 h and then vehicle for the final hour (n ϭ 9). Our laboratory has shown previously that this dose alters renal function in aldosterone-suppressed rats while inducing circulating concentrations within the physiological range (26). Urine samples were collected for the measurement of electrolytes and 3 H inulin.…”

Aldosterone Regulation of Protein Kinase Signaling Pathways and Renal Na+Transport by Non-genomic Mechanisms

“…One of the earliest reports of rapid actions of aldosterone on sodium transport in the kidney was in 1957 when Cole described the rapid effect of aldosterone administration for 30 min to cause a reduction in urinary loss of Na + and increased reabsorption by the renal tubules in response to intravenously administered saline in adult male rats [18]. It has also been documented that aldosterone infusion into aldosterone-suppressed rats (by adrenalectomy or infusion with sodium bicarbonate) resulted in the rapid increase in urinary Na + excretion [19]. The rapid non-genomic actions of aldosterone in vivo were further demonstrated in the intact rat when aldosterone induced a rapid increase in urinary Na + excretion within 15 min [20].…”