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G. D. THORBURN
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D. H. NICOL
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Prostaglandin F (PGF) is luteolytic in a number of species and the recent finding of endogenous secretion of PGF into the utero—ovarian vein of oestrogen-treated guinea-pigs (Blatchley, Donovan, Poyser, Horton, Thompson & Los, 1971) supports the hypothesis that PGF is the uterine luteolytic factor. Because the luteolytic effect of the uterus on the corpus luteum is local, it is necessary that a luteolysin secreted by one uterine horn can cause regression of the corpus luteum on the same side. The present experiments were designed to investigate the effect of PGF infused into the ovarian artery or uterine vein of the cyclic ewe.

Polyvinyl catheters (o.d. 0·8 mm) were inserted into a branch of one ovarian artery and a branch of the uterine vein on the same side in Merino ewes. The other ovary was removed. On day 6, 7, 8 or 9 of the succeeding

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J. M. BASSETT
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G. D. THORBURN
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DIANNE H. NICOL
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SUMMARY

Intravenous infusions of glucose into lambs in utero (130–150 days) and after birth, confirmed the marked post-natal increase in the magnitude of the response of plasma insulin to glucose. These studies also suggest that insulin secretion in foetal lambs is stimulated by glucose at lower plasma concentrations than in lambs after birth. The short-chain fatty acid, valeric acid, given as the sodium salt, caused a very rapid increase in the plasma insulin level of foetal lambs, when given either by intravenous injection or infusion. When birth was induced after only 135 days of gestation by i.v. infusion of a synthetic adrenocorticotrophin preparation (Synacthen) into foetal lambs there was also a prematurely induced maturation of the insulin secretory response to glucose. In these prematurely born lambs the insulin secretory response to i.v. glucose infusion was similar to that of normal lambs after birth and differed greatly from that of normal foetuses of similar age.

The results indicate that maturation of the insulin secretory mechanism in the lamb is associated with parturition and suggest that these changes may be consequences of the increasing corticosteroid secretion in the foetus during the last few days of gestation.

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