Pregnancy-induced increase of spinal cord peptide concentrations in rats

Tissue peptide concentrations of immunoreactive vasoactive intestinal peptide, somatostatin, substance P and cholecystokinin were measured by radioimmunoassay in undivided cervical, thoracic, lumbar and sacral segments of spinal cords from female Sprague Dawley rats either non pregnant or sacrificed at day 7, 14, 21, and 22 of pregnancy. Non pregnant animals showed for all peptides significant decreasing sacro-cervical gradients of tissue concentrations. Pregnancy was associated with significant rises of immunoreactive somatostatin concentration at the sacral level, and of immunoreactive VIP in the four segments tested. Peak values were recorded between day 14 and day 21, with a brisk decrease of VIP, but not of somatostatin, concentration on day 22. Sacrocervical gradients followed a biphasic increase, reaching a maximum on day 22. The concentrations of immunoreactive substance P and cholecystokinin remained stable throughout pregnancy. The present results suggest that the somatostatinergic and VIPergic structures stored in, or projecting to, the sacral autonomic nuclei are involved in the control of the anatomical and/or physiological modifications of the female genital tract during pregnancy.