Comparison of norepinephrine and serotonin vasoconstriction of the rat isolated testicular subcapsular artery at physiological and elevated transmural pressures

Abstract

This laboratory has previously described an in vitro preparation showing that the isolated testicular subcapsular artery of the adult rat has a novel triphasic transmural pressure-diameter myogenic response curve consisting of vasodilatation from 20 to 40 mm Hg, vasoconstriction from 40 to 100 mm Hg, and vasodilatation from 100 to 180 mm Hg, suggesting that the myogenic response of this artery between 40 and 100 mm Hg may have an important role in the autoregulation of the testicular blood supply. In the present studies, a 10-mm length of the adult rat isolated testicular subcapsular artery was cannulated and pressurized by an adjustable-height reservoir. External and internal arterial diameters were measured by a digital filar micrometer eyepiece. Dose-response curves for norepinephrine and serotonin were generated in a double-bath artery chamber at transmural pressures of 70 and 140 mm Hg, using half of the same artery for each pressure. Norepinephrine (3 x 10-8 to 1 x 10-5 M) produced a dose-dependent vasoconstriction at 70 mm Hg, with the highest dose causing a 31.4% decrease in lumen crossectional area (p < 0.05). Serotonin (3 x 10-8 to 1 x 10-6 M) produced a stronger dose-dependent vasoconstriction at 70 mm Hg, with the highest dose causing a 72.7% decrease in lumen cross-sectional area (p < 0.05). In marked contrast, the same concentration of norepinephrine and serotonin were found to have no statistically significant effect on the lumen cross-sectional area of the isolated testicular subcapsular artery at a transmural pressure of 140 mm Hg. It would therefore appear that the failure of homeostatic myogenic autoregulation of the adult testicular subcapsular artery at a transmural pressure of 140 mm Hg may not be compensated for by either a norepinephrine or serotonin-induced vasoconstriction of this artery. These data suggest the possibility that hypertensive blood pressures of 140 mm Hg or higher may cause myogenic autoregulatory failure resulting in a progressive vasodilatation of the testicular subcapsular artery, which may then produce a progressive increase in the blood supply to the testis that may culminate in hyperemia and edema of the testis.