A MODEL FOR STUDYING REGULATION OF ALDOSTERONE SECRETION - FRESHLY ISOLATED CELLS OR CULTURED-CELLS

Practically all studies relating to zona glomerulosa function have bee n performed either with freshly isolated cells or with cells used afte r 2 or 3 days in culture. This study compares the step-by-step respons e (binding, second messenger production and aldosterone response) of i solated glomerulosa cells vs cells maintained in primary culture to th e main stimuli of aldosterone secretion. One day in culture induces a decrease of 77 and 65% in the basal level of corticosterone and aldost erone secretions, compared to that observed in freshly isolated cells. In these conditions, the cells become more sensitive to most of their stimuli, but not all: e.g. important differences are noted in the dos e-response of aldosterone secretion to adrenocorticotropin (ACTH), whi ch is often shifted to a lower concentration sensitivity in cultured c ells. For example, 0.1 nM ACTH stimulates steroid secretion by three-f old in isolated cells while 1 pM ACTH already induces a 25 and nine-fo ld increase, respectively, in corticosterone and aldosterone output in cultured cells. Moreover, some stimuli such as isoproterenol do not h ave any effect in isolated cells but do stimulate steroid secretion in cultured cells. In contrast, other stimuli, such as serotonin or DA ( via DA, receptors) act preferentially in freshly isolated cells. The m ain observation derived from this study is that glomerulosa cells, und er appropriate conditions, are able to respond to their main secretago gues even after 4 days in culture. At this time, glomerulosa cells mai ntain their ultrastructural characteristics and functional properties and, aside from a few exceptions, demonstrate higher sensitivity to th eir known stimuli. Culture conditions used in the past 5 years have he lped demonstrate the regulatory role of a number of peptides which pro bably act via paracrine or autocrine pathways. However, the effects of certain stimuli must be studied in freshly isolated conditions since their respective receptor binding sites are lost in culture. In conclu sion, comparative studies between isolated and cultured conditions mus t be undertaken before pursuing studies on either the mechanisms of ac tion or interactions between newly identified regulators of aldosteron e secretion.