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ABSTRACT
Little is known about the cellular localisation of the angiotensin II (AII) type 1 receptor (ATI) in the rat adrenal glomerulosa cell, but some studies have suggested that receptor internalisation and recycling may occur.
Using a specific monoclonal antibody (6313/G2) to the first extracellular domain, we show here that most of the receptor is internalised in the unstimulated cell. When viable glomerulosa cells are incubated with 6313/G2, the receptor is transiently concentrated on the cell surface, and aldosterone output is stimulated. This stimulated output is enhanced by neither threshold nor maximal stimulatory concentrations of All amide, although the antibody does not inhibit All binding to the receptor. Conversely, the stimulatory actions of the antibody and those of ACTH are additive.
The data suggest that recycling to the plasma membrane is constitutive, or regulated by unknown factors. Retention of the ATI receptor in the membrane is alone enough to allow sufficient G protein interaction to generate maximal stimulatory events.
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Abstract
Several lines of experimentation suggest that a tissue-sequestered pool of 18-hydroxydeoxycorticosterone (18-OH-DOC) in the rat adrenal may be mobilized as an aldosterone precursor.
We show here that this steroid is maintained in a non-extractable form in the membranes of collagenase-dispersed fasciculata/reticularis cells. Because of this stability, the complex can be identified by immunocytochemistry and also, in IEF gels of solubilized inner adrenocortical zone membrane preparations, by immunoblotting. However, the complexed steroid cannot be extracted from the gels into organic solvent unless first treated with trypsin. Preincubation of viable whole glandular tissue with trypsin significantly enhanced aldosterone output and eliminated the trypsin-releasable 18-OH-DOC pool in IEF gels of solubilized inner zone membranes. Both prior sodium depletion and acute trypsin stimulation of whole glands enhanced extractable 18-OH-DOC in glomerulosa tissue membranes.
Other experiments using in situ hybridization show that mRNA coding for 11β-hydroxylase (which generates 18-OH-DOC) is confined to the inner adrenocortical zones, whereas aldosterone synthase (which does not) is transcribed exclusively in the glomerulosa.
The data suggest that a pool of 18-OH-DOC in inner zone membranes can be mobilized for utilization as an aldosterone precursor in the glomerulosa. The results also indicate the existence of an entirely novel tightly binding steroid carrier from which steroid cannot be extracted by organic solvent unless first subjected to proteolytic degradation.
Journal of Endocrinology (1995) 144, 359–368
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Abstract
The physiological factors which induce and maintain mammalian sperm maturation and motility generally remain unclear, although several agents are known to be involved. We describe here the application of immunocytochemical and immunoblotting methods to identify the angiotensin II type 1 (AT1) receptor in the tails of ejaculated rat and human sperm. Motility data on stimulated and unstimulated sperm from volunteers and patients attending fertility clinics showed that angiotensin II may increase both the percentage of motile sperm and their linear velocity, while the specific AT1 receptor antagonist DuP753 inhibited the action of angiotensin II on the percentage of motile sperm. In rat seminiferous tubules, AT1 receptors were present in primary spermatogonia and in spermatid tails, but immunoreactivity was not seen in sperm contained in caput or cauda epididymis, showing that AT1 receptor function is regulated during transit through the reproductive tract. Since local tissue reninangiotensin systems are present in both male and female tracts, the data suggest that angiotensin II has a role in the maintenance of sperm function and fertility.
Journal of Endocrinology (1995) 144, 369–
