Hypothalamic infusion of activin A increases water consumption and urine volume in the rat

Activin A immunoreactivity has been localized within the nucleus tractus solitarius and its projections into regions of the hypothalamus such as the paraventricular nucleus. However, the function of activin within the central nervous system is unclear. Because these regions of the brain are involved in the regulation of a variety of metabolic processes, we have measured body weight, food and water consumption, fecal mass, and urine volume in adult rats that received bilateral infusions of activin A into the dorsal hypothalamus near the paraventricular nuclei. Activin caused marked, parallel increases in water consumption and urine volume that were first apparent on days 3-4 and were maintained for the duration of the week-long infusions. There was no effect on water consumption or urine volume when the same doses of inhibin A or cytochrome c were infused, indicating that the effects of activin were specific and not due simply to infusion of protein into the hypothalamus. Furthermore, the effects of activin were selective for water consumption and urine volume, as neither activin, inhibin, nor cytochrome c had any effect on weight gain, food consumption, or fecal mass. Our results demonstrate that an activin A-containing neuronal system within the hypothalamus may have a role in the central regulation of fluid balance.