VASCULAR ACTIONS OF FUROSEMIDE AND BUMETANIDE ON RAT SUPERIOR MESENTERIC VASCULAR BED - INTERACTIONS WITH PROLACTIN AND PROSTAGLANDINS

The mesenteric vascular bed of the rat was used to investigate the effects of furosemide, bumetanide, prolactin, aspirin, indomethacin and prostaglandin E2 on the pressor response to norepinephrine. Furosemide, bumetanide and indomethacin could all inhibit the responses to norepinephrine: in each case responsiveness was restored by the addition of prostaglandin E2 to the perfusate. Bumetanide and furosemide both failed to inhibit responsiveness in the presence of an adequate amount (50 pg/ml) of prostaglandin E2. Ovine prolactin in a concentration of 50 ng/ml enhanced pressor responses to norepinephrine while 500 ng/ml, after an initial potentiation, inhibited responsiveness. Aspirin, furosemide and bumetanide all reversed both the potentiation produced by the lower prolactin concentration and the inhibition produced by the higher one. When taken in conjunction with other evidence these results suggest that the diuretics exert their vascular effects by inhibiting prostaglandin synthesis whereas prolactin acts by stimulating such synthesis.