Characteristics of a prompt morphodynamic response of the pineal gland to an acute ACTH injection.

The morphodynamic response of the pineal gland in the period 5-30 min after a single ACTH injection was studied. In 5 min a saline injection, functioning as a control, elicited a prompt release of the pineal active compounds advocated to be contained in clear vesicles and structures traditionally labeled lipid droplets. In the subsequent time period, 15 min, a rise in the relative volume of the granular endoplasmic reticulum (GER) and the Golgi apparatus, as well as prosecretory granules, was interpreted as a sign of an increased pinealocyte activity which leads to the restoration of the pineal gland endocrine potential. A decline in the increased mass of this membranous elaborative compartment in 30 min could be understood as an illustration of the stabilisation of the pinealocyte stress-evoked response. The ACTH injection did not apparently change the pattern of the morphodynamic pinealocyte response promoted by the saline injection in 5 min. However, starting from 15 min, a significant increase of the mass of GER and the Golgi apparatus was found in both pinealocyte populations. The augmented presence of prosecretory granules and lipid droplets, in comparison with the saline-injected animals in the respective time period, as well as the absence of a clearly observable evidence of the pinealocyte secretory activity pointed out that the ACTH stimulative action on the pinealocyte membranous elaborative compartment rather facilitated the pinealocyte endocrine recovery than supported their current secretory activity. From the functional viewpoint, the results obtained suggest that a stress-induced ACTH burst could modulate the post-secretory restitution of the endocrine potential of previously stress-activated pinealocytes.