Retinal angiography in divers.

OBJECTIVE: In the light of previous reports, to examine the possibility that professional diving might cause abnormalities of the retina and choroid. METHODS: The retinal fluorescein angiograms of 55 Royal Naval divers and 24 non-diver servicemen were compared. RESULTS: No differences were found between divers and non-divers and the prevalence of abnormalities was not correlated with diving experience. CONCLUSION: In contrast to previous reports, there seem, at least in naval personnel, to be no ocular consequences of diving.

Seasonal modification of ovine pineal function. 2. Steroidal effects on melatonin and prolactin profiles.

Pineal beta-adrenoceptor density and affinity in ewes are modified in a season-dependent manner by gonadal steroids and by the sympathetic innervation of the gland. The present study was undertaken to relate the steroidal effects on the receptors to post receptor endocrine events, and to investigate the influence of the sympathetic innervation of the pineal gland on these events. Plasma melatonin and prolactin profiles were determined during anestrus and during the normal breeding season in ewes subjected to sympathetic denervation of the pineal and/or a range of steroid-related treatments. Wherever valid comparisons could be drawn between effects of the treatments on beta-adrenoceptor variables and on circulating hormone levels, similar effects were noted. Further, ganglionectomy influenced hormone profiles similarly to estradiol under all conditions tested. It appears that gonadal steroids (estradiol) and the sympathetic neurotransmitter noradrenaline have opposing actions on prolactin levels, just as they have on pineal beta-adrenoceptor binding affinity. These findings suggest that steroid-mediated changes in receptor number and affinity are reflected in post receptor endocrine events. In addition, other factors (e.g. photoperiodic information transmitted via the sympathetic innervation) also play important roles in the regulation of the observed hormonal profiles. A steroid-mediated feedback regulation of pituitary prolactin release, partly direct and partly via pineal melatonin release, is suggested.

Seasonal changes in the sensitivity of ovine pineal beta-adrenoceptors to steroids.

Immunoneutralization of endogenous gonadal steroids has recently been shown to modify pineal beta-adrenoceptor function in intact Merino ewes. In the current study, interactions between gonadal steroids and these receptors have been further investigated. beta-Adrenoceptor density and binding affinity both showed time-related changes in ewes; the significance of these changes requires further study. Two observations, firstly modification of beta-adrenoceptor function by androstenedione and 17 beta-estradiol in ovariectomized, but not in intact ewes, and secondly that steroid-mediated effects on receptor density and binding affinity in the pineal of ovariectomized Merino ewes could be demonstrated during anestrus, but not during the breeding season for intact ewes, indicate that gonadal steroids may regulate pineal beta-adrenoceptor variables in Merino ewes. It is suggested that gonadal steroids may regulate ovine pineal function in ewes, and that the seasonal differences in sensitivity of luteinizing hormone release to steroid feedback may be mediated in part via effects on the pineal gland.

Sheep pineal beta-adrenoceptor function--interaction with gamma-aminobutyric acid.

To clarify the role and site of action of gamma-aminobutyric acid (GABA) in ovine pineal glands, we have investigated the effects of aminooxyacetic acid (AOAA), an inhibitor of GABA transaminase, on endogenous GABA content and beta-adrenoceptor mediated pineal function in Merino sheep. A significant elevation of endogenous GABA levels was noted in the glands, but no effect was observed on radioligand binding in vitro to pineal beta-adrenoceptors following in vivo administration of AOAA. Incubation of washed pineal membranes with GABA or AOAA had no effect on ligand binding to beta-adrenoceptors. Incubation of Merino pineal slices with GABA inhibited isoprenaline-stimulated but not basal serotonin N-acetyltransferase (NAT) activity. Incubation of whole pineal homogenates with GABA was without effect on either isoprenaline-stimulated or basal adenyl cyclase activity. Thus, Merino pineal glands resemble bovine pineals in that beta-adrenoceptor mediated melatonin biosynthesis in both species may be regulated in part by GABA. Our results indicate that GABA may exert its effect on Merino pineal NAT activity at a locus distal to the site of action of adenyl cyclase; however, the detailed mechanism and physiological role of this regulation remain to be elucidated.