Search Results

You are looking at 1 - 2 of 2 items for

  • Author: D R E Abayasekara x
  • Refine by Access: All content x
Clear All Modify Search
Restricted access

B J Whitehouse and D R E Abayasekara


The role played by cyclic AMP (cAMP)-dependent protein kinases (PKAs) in rat adrenal steroidogenesis has been investigated using cAMP analogues which show partial selectivity for the type I and type II PKA isoenzymes. These were aminohexylamino-cAMP (AHA-cAMP; selective for site 1 on type I PKA), N 6-benzoyl-cAMP (BZ-cAMP; selective for site 2 on PKA types I and II) and 8-thiomethyl-cAMP (TM-cAMP; selective for site 1 on type II PKA). Positive cooperativity exists between the two nucleotide-binding sites, thus the presence of type I PKA was inferred when synergistic increases in corticosteroid production were obtained with AHA-cAMP plus BZ-cAMP and that of type II PKA when synergistic increases were obtained with TM-cAMP plus BZ-cAMP.

The effects of AHA-cAMP, TM-cAMP and BZ-cAMP (10–100 μmol/l) on aldosterone production by glomerulosa cell preparations and corticosterone production by fasciculata/reticularis cell preparations were compared. Dose-related stimulation of steroid production was obtained with each cAMP analogue in both types of cell preparation. Experiments were performed using the cAMP analogues in combination at doses which gave minimal stimulation individually. Cells were incubated with AHA-cAMP (66 and 100 μmol/l) or TM-cAMP (15, 30 and 45 μmol/l) in the presence and absence of 15μmol BZ-cAMP/l. Synergistic responses were obtained with both analogue pairs in both cell types. The synergism ratio in fasciculata/reticularis cell preparations for the type I PKA selective pair of analogues (100 μmol AHA-cAMP/l plus 15μmol BZ-cAMP/l) was significantly higher (P<0·01) than that for the type II selective pair (45μmol TM-cAMP/l plus 15μmol BZ-cAMP/l; 7·9±1·2 (mean±s.e.m.) and 2·6±0·3 respectively). In zona glomerulosa preparations the ratio was higher (P<0·05) for the type II selective pair (1·6±0·1 for AHA-cAMP plus BZ-cAMP and 2·8±0·4 for TM-cAMP plus BZ-cAMP).

The effects of 100μmol AHA-cAMP/l and 45μmol TM-cAMP/l on the response to ACTH (1 pmol/l–10 nmol/l) were examined. Synergistic responses were obtained in fasciculata/reticularis cells with both analogues in combination with low concentrations of ACTH (10 and 100 pmol/l). In zona glomerulosa cells only the addition of TM-cAMP (45 μmol/l) in combination with 10 pmol ACTH/1 gave rise to synergistic increases in aldosterone production, which suggests that there may be some compartmentalization of the cAMP-dependent pathway in these cells.

The results indicate that both isoenzymes of PKA are present in rat adrenocortical cells and can play a part in the control of steroidogenesis. Type I PKA activity appears dominant in the control of zona fasciculata/reticularis cell function whereas modulation of type II PKA activity plays a more significant role in the responses of zona glomerulosa cells.

Restricted access

P R Riley, A P F Flint, D R E Abayasekara, and H J Stewart


A sheep endometrial oxytocin receptor (OTR) cDNA (1·5 kb) was isolated from a λ-ZAP library using a reverse transcription-PCR product probe generated from oestrous endometrial mRNA. The sheep OTR cDNA shared an overall similarity of 82% with human OTR cDNA, 85% with pig OTR cDNA and 76% with rat OTR cDNA. The encoded receptor was a 391 amino acid polypeptide 94% similar to human OTR, 94% similar to pig OTR and 93% similar to rat OTR. The sheep OTR contained two additional amino acids compared with human OTR which were located in the highly GC-rich third intracytoplasmic loop. This region is thought to be associated with G protein coupling and signal transduction. Expression of the cDNA in Cos-7 cells and measurement of oxytocin-induced phosphoinositide turnover confirmed that it coded for a functional product. The affinity of the expressed receptor was comparable with that observed for the in vivo receptor.