EFFECT OF MATERNAL INFUSION OF ADRENOCORTICOTROPHIN(1-24) (ACTH(1-24)) ON PARTURITION IN GUINEA-PIGS NEAR-TERM

While the mechanism of onset of labour in guinea-pigs is unknown, it h as been suggested that administration of adrenocorticotrophin(1-24) (A CTH(1-24)) near term induces labour. In order to verify this finding, guinea-pigs were fitted with indwelling carotid and jugular vascular c annulae. ACTH(1-24) (30 mu g h(-1) for four hours, n = 9) or vehicle ( n = 5) was infused intravenously on Day 64 (term is 68 days). ACTH(1-2 4) had no effect on gestational length (68.4+/-1.0 days, n = 6 v. cont rol, 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). Infus ion of ACTH(1-24) increased maternal ACTH concentrations from < 1.8 pm ol L-1 to 34+/-6 pmol L-1 (n = 6, P < 0.01) while fetal ACTH concentra tions remained undetectable (n = 6). Infusion of ACTH(1-24) increased cortisol concentrations in maternal plasma from 8.3+/-0.6 mmol L-1 to 15.8+/-0.8 mmol L-1 (n = 6, P < 0.001) but had no effect on concentrat ions of 13,14-dihydro-15-keto-PGF(2 alpha) (P = 0.8). It is concluded that (1) maternal infusion of ACTH(1-24) at the dosage used does not i nduce labour in guinea-pigs, and (2) ACTH(1-24) does not cross the pla centa.