1 The hypothesis that the relative vasoconstrictor ineffectiveness of prostaglandin E2 (PGE2) and PGF2,, on cerebral vessels of newborn pigs might be due to fewer receptors for these prostanoids was tested by comparing receptors for PGE2 (EP) and PGF2, (FP) in cerebral microvessels from newborn and adult pigs. 4 PGE2, 17-phenyl trinor PGE2 (EPI agonist), PGF2. and fenprostalene (PGF2, analogue) caused significantly less increase in inositol 1,4,5-triphosphate (IP3) in brain microvessels from the newborn than in those from adult pigs. The stimulation of IP3 by PGE2 and 17-phenyl trinor PGE2 was almost completely inhibited by the EP1 antagonist, AH 6809. 5 PGE2, 11-deoxy PGE, and M&B 28,767 produced small reduction of adenosine 3':5'-cyclic monophosphate (cyclic AMP) production in adult vessels but no effect in newborn tissues. 6 The lower density of EP and FP receptors in microvessels of newborn pigs compared to adults may explain the reduced ability of PGE2 and PGF2, to stimulate production of IP3 in tissues from newborn animals. This in turn, may provide an explanation for previous observations demonstrating that these prostanoids elicit contraction of adult cerebral microvessels, but exert minimal effects on these vessels in newborn animals.

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