PLASMA PROLACTIN LEVELS IN FEMALE RATS BEARING PARS DISTALIS OR TOTAL PITUITARY GLAND GRAFTS UNDER THE KIDNEY CAPSULE

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Abstract
The observation that the morphology of the ovaries of rats with pars distalis grafts differs considerably from that of the ovaries of rats bearing total pituitary gland grafts led to an investigation of plasma prolactin levels under both experimental conditions. Plasma prolactin levels of those rats with 2 partes distales grafted underneath the kidney capsule were significantly higher than those of control rats. There were no significant differences between prolactin levels of blood samples obtained 1, 2 and 3 mo. after the operation, although the prolactin levels appeared to decrease during the 2nd postoperative mo. Rats bearing 2 total pituitary gland grafts had large amounts of plasma prolactin with maximum values during the 3rd mo. after the operation. There were significant differences between prolactin levels of blood samples collected, 1, 2 and 3 mo. after the transplant of the total pituitary glands. The hypophysial graft which includes both the posterior and anterior lobes was far more effective in raising the plasma prolactin levels than the graft of the pars distalis only. Ultrastructural study showed that 3 mo. after the operation the predominant cell type in the pars distalis graft was the prolactin-secreting cell. These cells displayed the typical morphological features of cells producing large quantities of proteins for export. Grafts of the whole pituitary gland had 2 predominant cell types, the hypertrophied prolactin cells and other cells all with signs of a high rate of synthesis and release of their secretory product, probably melanocyte-stimulating hormone (MSH) cells. Since the presence of the 2nd cell type in the grafted tissue might be the trigger for the sustained and progressive increase in plasma prolactin levels in rats with total pituitary gland grafts, plasma MSH levels under these experimental conditions will have to be determined in future investigations.

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