Walter C. Adams

Effect of Purified Relaxin on Uterine Glycogen and Protein in the Rat

Summary Purified, electrophoretically homogeneous porcine relaxin (1750 GPU/mg) increased uterine glycogen in both unprimed and estrogen-primed ovariectomized rats. In estrogen-primed animals the glycogenic response was linear with the logarithm of the dose from 3 to 30 μg/animal; in unprimed animals the effect of 10 μg was essentially the same as that achieved with 30 μg. Relaxin also increased wet and dry uterine weights and total nitrogen content, indicating true uterine growth. Uterotrophic, as well as glycogenic effects occurred without estrogen priming, although synergism of the two hormones was observed; this suggests that relaxin receptor concentrations in the uterus may be, to some degree, estrogen dependent. Relaxin did not affect the concentrations of diaphragm glycogen or plasma glucose; thus the direct effects of relaxin appear to be limited to control of metabolic events in the female reproductive system in a manner similar to insulin regulation of general body metabolism.

Stimulation of rat uterine collagen synthesis by relaxin.

Abstract Immature, ovariectomized, estrogen-primed rats respond to the administration of porcine relaxin by an increase in the incorporation of labeled amino acids ([14C]leucine, [14C]phenylalanine, [3H]proline) into uterine proteins in vitro. The maximum response occurs about 12 hr after a single injection of 0.1 mg relaxin in benzopurpurine 4B solution; subsequently, the relaxin effect declines but is still apparent after 24 hr. Smaller, but still significant increases in incorporation rates can be induced by relaxin in the absence of estrogen priming. Uterine collagen synthesis, as indicated by the incorporation of [3H]proline and its conversion to hydroxyproline, appears to be a primary target of the relaxin stimulus, since the effect of relaxin upon proline incorporation into uterine collagen is significantly greater than its effect upon labeling of noncollagen protein.

Progesterone Inhibits the Uterotrophic Effect of Relaxin in Immature Rats

Abstract Injection of progesterone for 3 days before treatment with relaxin inhibited the trophic effect of the peptide in both estrogen-primed and unprimed uteri. The depression in collagen concentration and increase in apparent rate of proline incorporation into collagen induced by relaxin alone were also eliminated, indicating a fundamental blockade of the effect of relaxin in this experimental design as well as a close association of changes in collagen concentration with tissue hypertrophy. The effect of relaxin on incorporation of proline into soluble protein was not blocked by progesterone, however, suggesting a separate mechanism for this anabolic effect of relaxin.

Circulating hormone concentrations in hypothyroid rats with induced polycystic ovaries

Abstract The induction of polycystic ovaries in hypothyroid rats by human chorionic gonadotropin (hCG) has been studied for many years. A complete understanding of this phenomenon requires information regarding the circulating levels of the hormones of the hypophyseal-gonadal axis. In this study, serum prolactin (PRL), luteinizing hormone (LH), estradiol, testosterone, and progesterone were measured by radioimmunoassay at intervals during the 40-day period in which large ovarian cysts were induced in hypothyroid rats by daily injections of hCG. After 20 injections, ovaries increased in weight 10-fold, and well-developed ovarian cysts were present, accompanied by lutein tissue; cyst development continued for the subsequent 20 days of hCG. Both PRL and LH rose during the first 5 days of treatment and were maintained at high levels from day 20 on. The pattern of change of gonadal steroids showed greater increases with hCG in hypothyroid than in euthyroid rats. Levels of estradiol in hypothyroid, hCG-injected rats increased in parallel to ovarian hypertrophy, whereas progesterone was high in initial stages and then declined. Testosterone increased in both euthyroid and hypothyroid animals, with no clear pattern coincident with cyst formation. The data suggest that the formation of polycystic ovaries in the hypothyroid rat is associated with high levels of PRL and LH followed by elevations of estradiol, which may serve to maintain continuous PRL, as well as LH, stimulation of the ovary.

Effects of porcine relaxins upon uterine hypertrophy and protein metabolism in mice.

Abstract Two variant forms of porcine relaxin (B and C) are active in producing relaxation of the guinea pig pubic symphysis and in effecting uterine growth in rats. Only relaxin B, however, is active in the mouse pubic ligament assay. These two hormones were compared in mice for their effects upon uterine growth and incorporation of radioactively labeled proline into soluble protein and collagen in vitro and in vivo. Both relaxin B and relaxin C produced an early (3-hr) elevation in in vitro protein synthesis and a later (6-hr) increase in collagen incorporation of proline at the time when the uterotrophic effect was maximal. In vivo effects of relaxin C on the uterus were in some cases greater than relaxin B in contrast to the complete inactivity of the former upon the pubic ligament of the mouse. These findings suggest a high degree of tissue specificity for relaxin stimulation, a variability in responsiveness among tissues in the same animal, and perhaps a primary role of relaxin in uterine function with pelvic relaxation representing a secondary function which has developed in certain species.

The Response to Endogenous Relaxin of Guinea Pigs Refractory to Porcine Relaxin

Summary Guinea pigs made resistant to porcine relaxin by repeated injections were able to complete gestation and give birth to pups weighing the same as control animals. The progression of pelvic relaxation as gestation proceeded was retarded in the resistant animals although the optimum degree of relaxation was achieved just prior to parturition. Estrogen-primed, resistant animals responded to progesterone to the same extent as did controls, suggesting that the delay in pelvic relaxation during gestation is unlikely to be due to a reduction in secretion of relaxin or to a loss of tissue sensitivity to relaxin but rather to neutralization of pla-cental relaxin by circulating antibodies. Note added in proof. Dr. B. G. Steinetz, of Ciba-Geigy Corporation, Ardsley, N.Y., has demonstrated the existence of anti-porcine relaxin antibodies in the sera of the relaxin-resistant animals used in these experiments. The antibody content was measured by the ability of the serum specifically to bind 125I-poly-tyrosyl relaxin. Of the labeled relaxin added, 14 and 12%, respectively, was bound by 25 μl of serum from animals in groups II and III (Table I); the fraction bound by the same quantity of serum from control animals averaged less than 2%.

Comparison of systemic and uterine effects of relaxin and insulin in alloxan-treated, hyperglycemic rats.

Abstract The effects of porcine relaxin and insulin on blood glucose and on uterine and diaphragm glycogen were measured after 3 and 24 hr in alloxan-treated, hyperglycemic rats. Insulin caused a decrease in blood glucose and enhanced the glycogen concentration of diaphragm muscle but had no effect upon the uterus. Relaxin, which had no influence on blood glucose levels, increased uterine weight and uterine glycogen content; diaphragm glycogen concentration was depressed at 3 hr after relaxin administration. Neither insulin nor relaxin altered the action of the other hormone when given concurrently. Despite the structural similarities between insulin and relaxin, the two hormones exhibit distinctly different actions which were not found to overlap.

Effect of a Purified Porcine Relaxin Upon Glycogen and Protein in the Rat Uterus

The recent isolation (Sherwood and O’Byrne, 1974; Frieden et al., 1980) and characterization of porcine relaxin as a two-chain polypeptide bearing a distinct structural similarity to insulin (Schwabe and McDonald, 1977; James et al., 1977) has revived interest in an earlier report (Steinetz et al., 1950) that relaxin can exert glycogenic and protein anabolic effects in ovariectomized, estrogen- treated rats. Since the relaxins used in these early experiments were of relatively low specific activity (10–150 GPU/mg), we have examined the metabolic effects of purified, electrophoretically homogenous porcine relaxin as well as NIH-relaxin.