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Relaxin binding in the rat heart atrium.
P L Osheroff1, M J Cronin, J A Lofgren
1Department of Protein Chemistry, Genentech, Inc., South San Francisco, CA 94080.
Summary
Relaxin, a reproductive hormone, also binds to rat heart atria, suggesting new physiological roles beyond pregnancy. Cardiac relaxin receptor levels are independent of sex hormones, unlike those in the uterus.
Area of Science:
- Endocrinology
- Cardiovascular Physiology
- Reproductive Biology
Background:
- Relaxin, a reproductive hormone from the insulin family, has known binding sites in the rat uterus and brain.
- Previous studies suggested relaxin may possess physiological functions beyond its role in reproduction.
Purpose of the Study:
- To investigate the presence and characteristics of relaxin binding sites in the cardiac atrium.
- To compare the regulation of relaxin receptors in the heart versus the uterus.
Main Methods:
- Localization of 32P-labeled relaxin binding sites in rat cardiac atria.
- Competition assays using insulin, IGF-I, atrial natriuretic peptide, and angiotensin II.
- Analysis of relaxin binding in uterus and heart after gonadectomy and sex steroid administration.
Main Results:
- Specific and high-affinity relaxin binding was identified in the cardiac atrium of both male and female rats.
- Relaxin binding in the atrium was not affected by sex steroid hormones.
- Uterine relaxin binding decreased after ovariectomy but was restored by estrogen, unlike cardiac binding.
Conclusions:
- Specific, high-affinity relaxin receptors are present in the rat cardiac atrium.
- Cardiac relaxin receptors are regulated independently of sex hormones, contrasting with uterine receptors.