Effect of relaxin and somatotropin in combination with ovarian steroids on mammary glands in rats.

Abstract

Hypophysectomized-ovariectomized rats were injected sc daily for 19 days. Nine treatment groups (N = 10) included a sham control, bovine somatotropin (STH, 1 mg/day) alone or in various combinations with porcine relaxin (K, 90 GPU/day), estradiol benzoate (EB, 1 ag/day) and progesterone (P, 3 mg/day). Percent increase in body weights ranged from 3.0 percent for controls to 34.3 percent for the STH + R + P group, with the STH + R group (27.5 percent) significantly higher than STH alone (16.6 percent). In all cases, the addition of R to the treatment regimen significantly increased the percent change in body weight for that respective regimen. Indices for response of six abdominal-inguinal mammary glands included percent dry fat-free tissue, DNA and RNA weights, the latter two by chemical methods. Dry fat-free tissue weight as a percentage of wet weight was 4.6 percent in controls. All treatment groups were significantly higher than controls with ranges from 5.5 percent (STH) to 7.9 percent (STH + R + EB + P). DNA per 100 g body weight indicated’ that STH alone was mammogenic. Compared to control DNA (2.71 mg), STH alone (4.07 mg) and STH + R (4.35 mg) showed stimulatory responses of 1.5 and 1.6-fold, respectively. Highest observed DNA per 100 g body weight (5.58 mg) was in the combination of four hormones. Mammary RNA per 100 g body weight was increased significantly above controls (.70 mg) in all groups except STH + LB and STH + EB + R. Results indicated that STH + R had the ability to synergize with EB + P to grow the mammary gland.