Ultrastructural observations of somatotrophs following hypophysial portal vessel infusion of ouabain and a new growth horomone - releasing hormone



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Texas Tech University


A newly synthesized growth hormone - releasing hormone (GH-RH) was infused for one minute into the hypophysial portal vessels of the anterior pituitary of adult male rats. The somatotrophs were observed at ultrastructural level for morphological changes indicative of increased levels of emiocytosis and synthesis of new hormone. An identical experiment was done with the infusate being ouabain, a digitalis glycoside, which is a known pharmacological in-vitro secretagogue for growth hormone. At 1, 15, 30, and 60 minutes following infusion, the animal's anterior pituitary glands were removed and prepared for electron microscopic examination. Somatotrophs displayed marked emiocytic activity at 1 and 15 minutes and slight emiocytosis at 30 and 60 minutes in both the ouabain and GH-RH infused animals. The rough endoplasmic reticulum (RER) became dilated at 15 minutes and was maximally stimulated at 30 minutes in both groups. Activation of the Golgi complexes was observed at 15 and 30 minutes as evidenced by distended lamellae and formation of coated and smooth vesicles. At 30 and 60 minutes post-infusion, both the ouabain and GH-RH groups displayed an increase in dense lamellar bodies indicating an increase in lysosomal activity.

The findings from this study provide morphological evidence for the specificity of a new highly active GH-RH that stimulates both hormone synthesis and release in somatotrophs in-vivo. The morphological changes correspond to in- vitro and in- vivo studies with hypothalamic extracts and a commercially available decapeptide GH-RH. Ouabain stimulated both synthesis and release non-specifically in the anterior pituitary.