The calcium‐mediated promotion of mitotic activity in rat thymocyte populations by growth hormone, neurohormones, parathyroid hormone and prolactin

Abstract

Growth hormone, oxytocin, parathyroid hormone, prolactin and lysine vasopressin strongly stimulate mitotic activity in rat thymocyte populations maintained in vitro. These hormones have no mitotic effect on cells maintained in calcium-free medium. It is concluded that they stimulate mitosis only indirectly by sensitising the mitotically competent segment of a thymocyte population to the action of calcium. The stimulatory action of calcium itself is opposed by low concentrations of the mucopolysaccharide chondroitin sulphate. However, the inhibitory action of chondroitin sulphate can be overcome by growth hormone.A possible common mechanism of action of these hormones on mitotically competent cells is discussed.

Cyclic 3′-5′-adenosine Monophosphate: Its Possible Role in Mammalian Cell Mitosis and Radiation-induced Mitotic G2-delay

“…Although it has been reported that increased levels of calcium and magnesium facilitate the passage of irradiated thymocytes through S-phase, they do not affect mitotic G 2 delay (Whitfield, Rixon and Youdale 1969), in accordance with the results found for T-cells in this work. It is interesting that reducing the calcium level to one-quarter of the normal concentration (Scaife and Broh6e 1969) causes increased mitotic delay in T-cells although in HeLa cells the intracellular calcium levels are not affected by extracellular changes in calcium concentration (Borle 1968).…”

“…The hormone action is dependent on the availability of calcium, but can be mimicked by c-AMP (Whitfield, MacManus and Rixon 1970) and apparently is due to a stimulation of the entry of cells into the DNA-synthetic S-phase of the cycle. Radiation-induced mitotic delay in these cells has also been found to be diminished by the same agents and mechanism of action (Whitfield, Rixon and Youdale 1969). However, the relevance of such observations made with suspensions of the short-lived thymus lymphocytes to the control mechanisms, operating in rapidly-proliferating cultures of mammalian cells, is dubious.…”

“…Hormones may depress mitotic activity or initiate it in target tissues, generally as a result of gene activation (Borle andNeuman 1965, Bullough 1967). Various hormones, and elevated concentrations of calium and magnesium, have been shown to exert a mitogenic action on thymus lymphocytes Youdale 1969, Whitfield, Perris and. The hormone action is dependent on the availability of calcium, but can be mimicked by c-AMP (Whitfield, MacManus and Rixon 1970) and apparently is due to a stimulation of the entry of cells into the DNA-synthetic S-phase of the cycle.…”

Neurohypophysial Receptor Gene Expression by Thymic T Cell Subsets and Thymic T Cell Lymphoma Cell Lines

“…Similarly to what has been shown for IGF type 2 receptors (CD222) (Mason, 2000), it may be expected that OTR and V3R also will be soon identified as new cluster differentiation (CD) markers. Ancient studies have reported that neurohypophysial ligands increase thymocyte growth (Whitfield et al, 1969;Martens et al, 1992) and the level of glucose oxydation in the thymus (Goren et al, 1984). More recently, the binding of neurohypophysial ligands, particularly OT, was shown to increase the level of inositol triphosphate and to phosphorylate focal adhesion-related kinases (FAK) in immature T cells .…”

The Thymic Repertoire of Neuroendocrine-Related Self Antigens: Biological Role in T-Cell Selection and Pharmacological Implications

“…Interestingly, the expression of the rat V1b (or V3) receptor was recently identified in tissues outside the anterior pituitary, including the thymus [41]. Already in 1969, the mitogenic effect of neurohypophysial peptides on rat thymocytes was described [42], where-Geenen/Kecha/Brilot/Charlet-Renard/ Martens as OT was reported to stimulate glucose oxidation by rat thymocytes [43]. On the basis of antagonist effects, murine pre-T cells express a V1 (or V3) subtype of neurohypophysial receptor, while mature cytotoxic T cells harbor receptors of the OT type; this observation suggests that the neurohypophysial reception system expressed by T lymphocytes could 'mature' in parallel with their stage of differentiation.…”