Effect of maternal infusion of adrenocorticotrophin1 - 24(ACTH1 - 24) on parturition in guinea-pigs near term

Abstract

While the mechanism of onset of labour in guinea-pigs is unknown, it has beensuggested that administration ofadrenocorticotrophin_1-24(ACTH_1-24) near term induces labour. In order to verifythis finding, guinea-pigs were fitted with indwelling carotid and jugularvascular cannulae. ACTH_1-24 (30 µgh^-1 for four hours, n = 9)or vehicle (n = 5) was infused intravenously onDay 64 (term is 68 days). ACTH_1-24 had no effect ongestational length (68·4 ± 1·0days,n = 6 v. control,69·6 ± 0·3 days, n = 5,P = 0·8). Symphysial width, fetal weight,number and viability were similar in both groups (all P> 0·1). Infusion of ACTH_1-24 increasedmaternal ACTH concentrations from <1·8 pmolL^-1 to 34·6 pmol L^-1(n = 6, P < 0·01) while fetal ACTHconcentrations remained undetectable (n = 6).Infusion of ACTH1 24 increased cortisol concentrations in maternal plasma from8·3 ±0· 6 mmol L ^-1 to 15·8± 0·8 mmol L^-1 (n= 6, P < 0·001) but had no effect onconcentrations of 13,14-dihydro-15-keto-PGF_2α(P = 0·8). It is concluded that(1) maternal infusion of ACTH_1-24at the dosage used does not induce labour in guinea-pigs, and(2) ACTH_1-24 does not cross the placenta.