Messenger RNA Dependent Synthesis of a Protein Containing Relaxin Related Sequences

Abstract

Serum relaxin levels in pregnant rats, sows, and guinea pigs are very low during most of gestation (Sherwood et al. 1975); mean relaxin concentrations in the sow range between 0.1 and 2.0 ng/ml throughout the first 100 days of pregnancy. During this period small electron dense cytoplasmic granules begin to appear in luteal cells. This granule population continued to increase in late gestation, reaching a maximum several days before parturition. About 24–48 hours before delivery a rapid disintegration of the cytoplasmic granules occurs. Serum levels of relaxin rise rapidly and then drop precipitously during parturition and lactation (Belt et al.3 1971). Studies in rat ovarian homogenates also suggest a steady, gradual rise in relaxin production throughout pregnancy (Sherwood and Crnekovic, 1979). The stimuli for the initial production of the hormone, the factors controlling its secretion and storage during pregnancy, and the reasons for its explosive release at term remain obscure. Relaxin has traditionally been assigned to the class of pregnancy-related hormones, but at least one study suggests that in humans the protein is also present in non-pregnant sera (Bryant-Greenwood et al.3 1977).