PATTERNS OF RELAXIN AND STEROIDS IN THE REPRODUCTIVE-CYCLE OF THE COMMON MARMOSET (CALLITHRIX-JACCHUS) - EFFECTS OF PROSTAGLANDIN-F2-ALPHA ON RELAXIN AND PROGESTERONE SECRETION DURING PREGNANCY

We measured the concentrations of relaxin (Rlx), progesterone, and est radiol-17 beta in serum samples obtained twice or three times weekly f rom marmosets during the estrous cycle and pregnancy. The cyclic patte rns and concentrations of progesterone and estradiol-17 beta were simi lar to those reported by previous investigators. Rlx was not detected in individual serum samples (< 0.62-1.25 ng/ml) obtained from nonpregn ant marmosets. However, pooling of luteal serum from all animals permi tted assay of much larger volumes of serum (0.4 mi vs, 0.1 ml), and a concentration of about 1 ng/ml was detected. Rlx was first detected in serum in the second or third week of the 21-wk marmoset pregnancy, ro se to a peak during Weeks 10-14, and then declined slowly as the time of parturition approached. The pattern of Rlx was unlike that observed during pregnancy in Old World monkeys, chimpanzees, or women, and res embled, instead, that seen in rodents, carnivores, and equids. Progest erone and estradiol-17 beta likewise increased throughout pregnancy, a nd their patterns were similar to those previously described for marmo sets by other investigators. The concentrations of the steroids and Rl x in serum of pregnant marmosets was 10-fold or more higher than those found in Old World monkeys, baboons, chimpanzees, or women. Spontaneo us abortions in two of the marmosets were accompanied by precipitous f alls in serum levels of progesterone, estradiol-17 beta, and Rlx. Foll owing s.c. injection of the luteolytic agent prostaglandin F-2 alpha ( PGF(2 alpha)) into two marmosets at midpregnancy, serum progesterone a nd Rlx fell to low levels. These animals received a progestin, 17 alph a-ethyl-19-nortesterone,to preclude abortion. Serum progesterone rose again, but serum Rlx remained low for the duration of pregnancy. Deliv ery of normal young occurred at the expected time in each of the PGF(2 alpha)-treated marmosets. The reduction of circulating Rlx to low lev els did not adversely affect either the maintenance or the outcome of the pregnancies.