Micropuncture study of avian kidney: effect of prolactin

Renal function was studied in anesthetized European starlings (Sturnis vulgaris) by micropuncture and clearance techniques. A previous study had shown some changes in the renal function of birds in molt. Endogenous prolactin levels have been shown to be elevated at this time. In the present study, renal function was studied during the infusion of an isotonic sodium chloride solution and then when ovine prolactin was added to the infusion. Ovine prolactin resulted in an elevation of plasma urate concentration but had no significant effects on other plasma parameters or on the concentration of the various ions in tubular fluid samples. Urine flow rate was significantly higher during prolactin infusion, although whole animal glomerular filtration rate, single nephron glomerular filtration rate, and the percentage fluid reabsorption in the proximal tubule (up to the point of micropuncture) were unaltered. The whole animal fractional excretions of sodium and chloride were significantly higher, those of magnesium and potassium were significantly lower, and the fractional excretion of phosphate tended to be lower during prolactin infusion. At the level of the proximal tubules of the reptilian-type nephrons, prolactin infusion caused a slight reduction in the net reabsorption of sodium and chloride. Therefore the main effects of prolactin on renal function are occurring in the distal nephron of the reptilian-type nephrons or in the mammalian-type nephrons. It appears that prolactin may affect renal function in avian species and that these actions may be modulated by a range of factors as has been demonstrated in mammals.