The Effect of Unit Gravity Sedimentation on Adrenal Steroidogenesis by Isolated Rat Glomerulosa and Fasciculata Cells

To assess the mechanisms by which regulatory factors control aldosterone secretion, a purified adrenal glomerulosa cell system, sensitive to physiological concentrations of agonists is of critical importance. We have evaluated the feasability of using a unit gravity sedimentation technique to achieve this objective.

Although basal aldosterone and corticosterone levels fell to 20% and 35% of the values in unsedimented cells, respectively, adrenal glomerulosa cells purified by unit gravity sedimentation demonstrated the same threshold sensitivity to angiotensin II (2.4 × 10⁻¹⁰m) and potassium (4.3 meq/liter) as unsedimented cells. In contrast, the threshold sensitivity of the sedimented cells to α-ACTH-(l–24) (3.5 × 10⁻¹¹m) was one tenth that observed in the unsedimented glomerulosa cells.

Regardless of the method of preparation, fasciculata cells did not respond to either angiotensin II or potassium, while sensitivity to ACTH was established at 3.5 × 10⁻¹²m, and the cells reached a maximum corticosterone output of 1600% of control at 3.5 × 10⁻⁹m ACTH in both sedimented and unsedimented fasciculata cells.

The fall in steroid basal output of glomerulosa cells after sedimentation was not due either to an alteration in cellular biosynthesis, since the cells’ sensitivity to angiotensin II and potassium was unchanged, or to removal of in vivo stimuli, since basal angiotensin II levels were the same in both preparations. On the other hand, both the production of corticosterone and the conversion of corticosterone to aldosterone was reduced more than 40% in the sedimented cells. Thus, the reduction in basal aldosterone output and adrenal responsiveness to ACTH was probably due not to damage to the cells but to reduction in precursor (corticosterone) concentration because the contaminating corticosterone-producing fasciculata cells were eliminated. Since corticosterone also modifies the activity of the enzymes necessary to convert corticosterone to aldosterone, a further reduction in aldosterone output was produced. (Endocrinology106: 50, 1980)