Lack of control of renin release by adrerfergic nervous system in the aglomerular toadfish

Abstract

Aglomerular toadfish, Opsanus tau, release renin in response to hemorrhage or vasodilator drugs, presumably by stimulating a renal arterial baroreceptor. We aimed to determine whether the adrenergic nervous system and prostaglandins play a role in the control of renin release in unanesthetized toadfish kept in 50% seawater. Isoproterenol (1 μg/kg) increased plasma renin activity (PRA) fourfold and decreased blood pressure (BP); both effects were abolished by a concomitant infusion of propranolol. Propranolol itself slightly decreased the basal level of heart rate and- BP, but not that of PRA. Norepinephrine (1 μg/kg) increased BP, but did not change PRA. Repeated injection of 6-hydroxydopanune did not alter resting levels of either PRA or BP. Monoamine-speck nerve fluorescence activity could not be demonstrated in association with arterioles of kidneys from intact toadfish or from those treated with monoamine oxidase inhibitor and norepinephrine (5 mg/kg). Furthermore, treatment of toadfish with indometbacin (10 or 20 mg/kg) prevented neither the increase in PRA nor the reduction in BP after a massive hemorrhage. These results indicate that renin release in toadfish primarily occurs in response to a reduction in renal arterial pressure, whereas it appears unlikely that the adrenergic nervous system or prostaglandins have a significant role in the control of renin release.