Effect of a brief stress on progesterone plasma levels in pregnant and non-pregnant guinea pigs

Abstract

Steroid hormones are essential for vertebrate reproduction. They are involved in the regulation of major female reproductive events like ovulation, embryo implantation, or gestation. For instance, progesterone promotes foeto-maternal exchanges whereas glucocorticoids stimulate the mobilization of the required energy resources. However, glucocorticoids are key effectors of the stress response; chronic elevations of these hormones can exert negative effects on reproduction. Yet, little is known about the effects of a brief exposure to a stressor on the respective plasma concentrations of sex steroids and glucocorticoids, notably during pregnancy. We examined the impact of a brief stress (handling + 1.5 hours in a bag) on progesterone and cortisol plasma concentrations in pregnant and non-pregnant female guinea pigs. Analyses revealed that: 1) pregnant females exhibited higher baseline progesterone and cortisol concentrations compared to non-pregnant females, as expected; 2) cortisol concentrations increased rapidly following manipulation, revealing a typical hormonal stress response; and, 3) progesterone concentrations decreased on average by 50.9% following the brief stress period, both in pregnant and non-pregnant individuals. These experimental results show for the first time a drastic and rapid impact on progesterone concentration caused by a brief stress.