Cell swelling (induced by hypotonicity or permeants) evokes exocytosis of material stored in secretory vesicles resulting in a secretory burst of peptide hormones or enzymes from various types of cells. Dynamics of this secretion is indistinguishable from that induced by specific secretagogue. Swelling-induced secretion possesses specific features indicating a unique signaling pathway. For instance glucose- and swelling induce insulin secretion through separate signal transduction pathways; hyposmotic stimulation is independent from the extra- and intracellular Ca²⁺ , does not involve other intracellular mediators of glucose stimulation, and could not be inhibited by noradrenaline. Swelling is a useful tool when natural or pharmacological secretagogue is unknown: Thyrotropin releasing hormone (TRH) release from the heart slices could be stimulated by hypotonic medium and stimulation overrides inhibitory effect of angiotensin II. Cell swelling-induced exocytosis possesses limited selectivity; cells specifically involved in water and salt regulation retain their specific response to osmotic stimuli: hypotonic medium evokes TRH but not oxytocin release from hypothalamic paraventricular nucleus (PVN). Specific response of intranuclear oxytocin secretion to osmotic stimulation in the PVN and the supraoptic nucleus could be obviated by GdCl₃ and at these conditions general response (hormone release) to swelling-inducing stimuli emerged. Swelling-induced hormone secretion could have pathophysiological implications. In ischaemia there is a shift to anaerobic glycolysis and production of metabolites which can increase the intracellular osmolarity by 130 mOsmol.L^-1 after 60 min, thus producing cell swelling. Peptides and proteins released after swelling could play an important role in the pathophysiology of ischaemia and be mediators of local or remote preconditioning when factors released at the place of ischaemia have protective effect.

Supported by grants of VEGA 2/6158/26, APVV 0235-06, and the project of CE SAV CENDO