Papillary plasma flow in rats. II. Hormonal control.

Abstract

Papillary plasma flow (PPF) was measured by the albumin accumulation technique in Wistar rats. PPF was significantly lower in male (293 +/- 5 microliter X min-1 X g-1) than in female (499 +/- 17) rats. Castration in male rats increased PPF; testosterone administration in gonadectomized rats returned PPF to control. Acute indomethacin administration equalized PPF in both sexes to low values close to those found in normal males (320 +/- 5 in males, 326 +/- 17 in females). Conversely, captopril administration equalized PPF in both sexes by raising PPF in males (505 +/- 21) without significant change in females (526 +/- 88). Dehydration decreased PPF slightly in males (255 +/- 28) but more markedly in females (349 +/- 11). This decrease was prevented by captopril administration (520 +/- 34 and 609 +/- 61 in males and females, respectively). In captopril-treated male rats, angiotensin II (AII) was continuously infused by osmotic minipumps at a rate of 5 micrograms/h. This did not restore PPF (405 +/- 12) to basal values. In contrast, AII infusion together with indomethacin administration completely restored PPF (322 +/- 22) in captopril-treated rats whereas indomethacin alone did not normalize PPF (425 +/- 18). We suggest that male sex hormones and AII decrease PPF, and account for the low PPF measured in male rats. Vasodilator PGs are involved in the high PPF found in female rats. The vasodilator action of captopril on papillary circulation is explained by both decreased AII formation and increased PG synthesis.