Relaxin: a mammotropic hormone promoting growth and differentiation of the pigeon crop sac mucosa.

The pigeon crop sac is responsive to local administration of mammotropic hormones independently of systemic hormonal influences. We showed previously in mice that relaxin promotes growth of the mammary gland only after pre-treatment with estrogen. In this study we investigated whether relaxin, locally administered, has a stimulatory effect without estrogen pre-treatment. The results of this study show that relaxin stimulates the crop sac mucosa causing changes in its gross appearance and histological modifications indicating enhanced growth and differentiation of the mucosal epithelium. The effects of relaxin are dose-related, as demonstrated by the increases of the wet and dry weights, the [3H]thymidine and [3H]uridine uptakes of the mucosa, and the histochemically detectable DNA content of the mucosal epithelium. These results strengthen the idea that relaxin should be included in the list of mammotropic hormones.