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Ovulation induced by hCG in rabbits was reduced significantly (P less than 0.005) by sulpiride-induced hyperprolactinaemia. The pre- and post-ovulatory increases in peripheral and ovarian venous progesterone (but not oestradiol or testosterone) were suppressed in the treated animals. The condition of hyperprolactinaemia also prevented the usual changes in 2,4-dinitrophenyl-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg-OH peptidase (DNP-peptidase) and alpha-N-benzoyl-DL-Arg-beta-naphthylamide hydrolase (BANA-hydrolase) activities in follicular tissue that had been stimulated by an ovulatory dose of hCG. These results suggest that inhibition of progesterone production and collagenolytic enzyme activity by sulpiride-induced hyperprolactinaemia may be responsible for the ovulatory dysfunction that occurs when a mammal has a high level of circulating prolactin.

ABSTRACT-The effects of potassium channel openers NIP-121 ((+)-7,8-dihydro-6,6-dimethyl-7-hydroxy-8-(2-oxo-piperidine-1-yl)-6H-pyrano[2,3 f]benz-2,1,3-oxadiazole) and levcromakalim were examined in vitro and in vivo. In isolated canine vascular beds, NIP-121 (3 x 10-9 to 10' M) and levcromakalim (3 x 10-8 to 10-6 M) produced a concentration-dependent reduction in the vasoconstrictor responses to U46619. The effects were antagonized by glibenclamide, an ATP-sensitive potassium channel blocker. The maximal relaxation was more than 70% of the maximal vasodilation induced by papaverine (10-'M), except in the basilar artery. These compounds had very potent effects on the coronary and cranial mesenteric arteries and saphenous vein. In the coronary perfused rat heart, both compounds (10-' M) also increased coronary perfusion flow. The effects were also inhibited by glibenclamide (10-6 M). In anesthetized dogs, NIP-121 (1 to 10 t€g/kg (3.2 to 32 nmol/kg), i.v.) and levcromakalim (3 to 30 tag/kg (10.5 to 105 nmol/kg), i.v.) dosedependently increased coronary and renal blood flow. NIP-121 and levcromakalim at higher doses produced the greatest increase in coronary blood flow among the blood vessels examined, in spite of the hypotensive effect. In conclusion, NIP-121 and levcromakalim were similarly selective vasodilators on the canine isolated coronary and cranial mesenteric arteries and saphenous vein, and they selectively increased coronary blood flow in vivo. With respect to increasing the coronary blood flow, NIP-121 had a fourfold greater potency than levcromakalim. This effect might be related to the glibenclamide-sensitive potassium channels.

Changes in plasma cholecystokinin (CCK) levels after feeding were investigated in dairy cows. Three Holstein-Friesian lactating cows given concentrates at 06.00 and 13.00 h and hay at 16.30 h were used. Blood samples were taken from the jugular vein from 0 (before feeding, 13.00 h) to 6 h at 1-h intervals. The immunoreactivity of CCK was expressed in terms of the CCK-8 equivalent. The plasma concentration of CCK was not changed over the experimental period. This result might be reflected by the continuous flow of digesta from the rumen.

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