Prolactin and the rat kidney: a clearance and micropuncture study.

PRL is a pituitary hormone with important osmoregulatory properties in lower vertebrates and has been reported to decrease renal water and electrolyte excretion in mammals. Although several studies have suggested that the proximal tubule is the major site of action of PRL, no direct examination of such an effect has been made. In the present study we used micropuncture and clearance techniques to examine the effect of ovine PRL (oPRL) infusion on single nephron and whole kidney function in anesthetized volume-expanded rats pretreated with bromocriptine to suppress endogenous PRL release. oPRL infusion was associated with a significant reduction in urinary sodium, potassium, and water excretion compared to changes seen in the control group. There was no significant effect of oPRL on whole kidney glomerular filtration rate, renal plasma flow, filtration fraction, renal blood flow, renal vascular resistance, or arterial pressure compared to those in control rats. Single nephron studies failed to detect any significant effect of oPRL on single nephron glomerular filtration rate and absolute or fractional reabsorption by the proximal convoluted tubule. Although arginine vasopressin was detected in the oPRL preparation, the quantity infused was negligible compared to the plasma levels found in anesthetized rats prepared for kidney micropuncture. Our results suggest that oPRL exerts a renal tubular action separate from arginine vasopressin to decrease water and electrolyte excretion which occurs beyond the last superficial convolution of the proximal convoluted tubule.