Signals controlling renin release in aglomerular toadfish

Area of Science:

• Comparative physiology
• Renal physiology
• Endocrinology

Background:

• Toadfish (Opsanus tau) possess unique renal anatomy, lacking glomeruli and macula densa, yet exhibit high renin activity.
• A pressure- or volume-sensitive mechanism controls renin release in toadfish, triggered by blood pressure or volume reduction.
• The roles of beta-adrenergic receptors and calcium influx in toadfish renin release remain unclear.

Purpose of the Study:

• To investigate the involvement of beta-adrenergic receptor-mediated activation in toadfish renin release.
• To determine if calcium influx underlies the baroreceptor mechanism controlling renin release in toadfish.
• To elucidate the cellular mechanisms governing renin secretion in the toadfish kidney.

Main Methods:

• Administered isoproterenol and propranolol to unanesthetized toadfish to assess beta-adrenergic effects on blood pressure and plasma renin activity (PRA).
• Utilized in vitro superfusion of toadfish renal slices to measure renin secretion under varying conditions.
• Applied high potassium (K+) and nifedipine to renal slices to investigate the role of calcium influx in regulating renin secretion.

Main Results:

• Isoproterenol injection decreased blood pressure and increased PRA, effects abolished by propranolol, but basal PRA was unaffected.
• High K+ significantly suppressed renin secretion from renal slices.
• Nifedipine restored K+-suppressed renin secretion, while isoproterenol had no effect on basal or K+-suppressed secretion.

Conclusions:

• Calcium influx appears to mediate inhibitory signals for renin secretion in toadfish.
• Beta-adrenoceptor-mediated activation of granulated cells does not seem to play a significant role in toadfish renin release.
• The findings suggest a distinct cellular mechanism for renin control in toadfish, differing from mammals.