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Evidence for a novel source of relaxin: atrial cardiocytes
1Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Iowa State University, Ames 50010.
Insights
Atrial cardiocytes, heart cells in rat atria, secrete the hormone relaxin. This finding suggests relaxin may regulate cardiovascular function through local signaling pathways.
Area of Science:
- Cardiovascular Biology
- Endocrinology
- Cell Biology
Background:
- Relaxin is an insulin-like hormone with known cardiovascular effects.
- Specific relaxin receptors are present in rat atria, but the source of endogenous relaxin was unclear.
Purpose of the Study:
- To investigate whether atrial cardiocytes can secrete relaxin.
- To determine the cellular source of atrial relaxin.
Main Methods:
- Reverse hemolytic plaque assay using antibody-directed, complement-induced erythrocyte lysis.
- Culture of neonatal rat atrial cardiocytes in monolayers.
Main Results:
- Approximately 33% of cultured atrial cardiocytes secreted detectable immunoreactive relaxin.
- Sustained secretion of relaxin was observed over 3 hours of incubation.
- Plaque area, indicating cumulative secretion, increased by 31% from 1 to 3 hours.
Conclusions:
- Atrial cardiocytes are a source of endogenous relaxin in the rat atrium.
- Relaxin may act on the cardiovascular system via autocrine or paracrine mechanisms.
Abstract:
Antibody-directed, complement-induced erythrocyte lysis (reverse hemolytic plaque assay) around atrial cardiocytes was used to determine whether this cell type possesses the capacity to secrete the insulin-like hormone relaxin. After 2h of incubation, 33 +/- 4% (n = 3) of cardiocytes derived from the atria of neonatal rats secreted detectable amounts of immunoreactive relaxin (i.e. formed plaques) when cultured in monolayers. Increased culture time of cardiocytes failed to increase the fraction of cardiocytes that secreted relaxin. The cumulative amount of relaxin secreted after 3h of incubation (plaque area) was 31% greater (P < 0.05) than the amount of hormone present after 1h of incubation, evidence of sustained peptide secretion by cultured cardiocytes. These data suggest that the source of the endogenous ligand for the specific and high-affinity relaxin receptors located in rat atria is the atrial cardiocyte itself. Therefore, relaxin may act via autocrine and/or paracrine routes to regulate cardiovascular structure and/or function.