Progesterone rapidly reduces arterial pressure in ewes

Area of Science:

• Reproductive endocrinology
• Cardiovascular physiology
• Neuroendocrinology

Background:

• Chronic progesterone treatment lowers mean arterial pressure (MAP) and expands plasma volume.
• Progesterone metabolites may exert rapid, non-genomic effects on the baroreflex.
• Understanding these rapid effects is crucial for comprehending progesterone's physiological roles.

Purpose of the Study:

• To investigate the rapid effects of progesterone on MAP, sodium levels, arginine vasopressin, and baroreflex sensitivity in ewes.
• To determine if progesterone's effects are dose-dependent and mediated by non-genomic mechanisms.
• To explore potential interactions between progesterone and the baroreflex under physiological and supraphysiological conditions.

Main Methods:

• Ewes received 2-hour infusions of vehicle or progesterone at 3 or 6 µg/kg/min.
• Measurements included MAP, plasma Na+, arginine vasopressin, and baroreflex sensitivity.
• Analysis focused on rapid changes occurring within minutes of infusion initiation.

Main Results:

• Progesterone infusion at 3 µg/kg/min, mimicking ovine pregnancy levels, significantly reduced MAP by 17 minutes.
• This rapid reduction suggests a non-genomic mechanism of action.
• Progesterone at 6 µg/kg/min (supraphysiological) did not alter MAP, and overall baroreflex sensitivity remained unchanged.
• A trend towards attenuated tachycardic response to hypotension was observed at the higher dose.

Conclusions:

• Progesterone can rapidly decrease MAP via non-genomic pathways at physiologically relevant concentrations.
• The lack of a linear dose-response suggests complex interactions involving multiple progesterone receptor populations.
• Further research is needed to elucidate the specific mechanisms and receptor subtypes involved in progesterone's rapid cardiovascular effects.