Role of cyclic anp in the regulation of serotomin N-acetyltransferase in retina

Abstract

A rabbit polyclonal antiserum was raised against bovine serum transferrin (TF) and used to construct a homologous radioimmunoassay which measures bovine TF in the range 0.16–4.00 μg/ml. TF is a transport protein which is believed to supply iron to developing germ cells which reside beyond the blood-testis barrier. The assay was used to monitor TF secretion by cultures of Sertoli cells which were isolated from 3–4-month-old Hereford calf testes and maintained in culture for up to four days. The cells were treated with a range of hormones and growth factors in serum-free medium to determine which factors regulate the secretion of TF.Basal levels of TF secretion were low (0.16–0.26 μg/ml); however, major increases (8-fold; P < 0.001) in the secretion of TF were induced by bovine follicle-stimulating hormone (FSH; half-maximal response (ED50)=310 ngUSDA-bFSH-Bl/ml) and by the more purified ovine FSH (ED50=5.5 ngNIADDK-oFSH-16/ml). The nucleotide analogue 8-bromo-cyclic adenosine monophosphate (8Br-cAMP) also evoked a 9-fold increase in TF secretion (ED50=0.71 mmol/l), indicating that the FSH response was mediated via the activation of adenylate cyclase. Significant increases in TF secretion of a lesser magnitude were also induced by epidermal growth factor (EGF; 121% at 500 ng/ml), insulin (348% at 20 IU/ml), and retinol (531% at 500 ng/ml) and all three agents augmented the TF response to FSH. In contrast, testosterone (500 nmol/l) showed only a 55% stimulation of TF secretion, and all other steroids (5α-DHT, oestradiol-17β, cortisol, progesterone) and protein hormones tested: bovine luteinizing hormone (⩽ 50 ng NIAMMD-bLH-4/ml) prolactin (⩽ 100 ng NIAMMD-bPRL-6/ml) and glucagon (⩽ 2 μg/ml) were without significant effect. These experiments show that both hormones (FSH, insulin) and growth factors (EGF, retinol) regulate TF secretion in the bovine Sertoli cell.