Presence of thyrotropin-releasing hormone in porcine and bovine retina

Hypothalamic neurohormones and immune responses

The aim of this review is to provide a comprehensive examination of the current literature describing the neural-immune interactions, with emphasis on the most recent findings of the effects of neurohormones on immune system. Particularly, the role of hypothalamic hormones such as Thyrotropin-releasing hormone (TRH), Corticotropin-releasing hormone (CRH) and Gonadotropin-releasing hormone (GnRH). In the past few years, interest has been raised in extrapituitary actions of these neurohormones due to their receptors have been found in many non-pituitary tissues. Also, the receptors are present in immune cells, suggesting an autocrine or paracrine role within the immune system. In general, these neurohormones have been reported to exert immunomodulatory effects on cell proliferation, immune mediators release and cell function. The implications of these findings in understanding the network of hypothalamic neuropeptides and immune system are discussed.

Dopaminergic receptors in bovine retina and their interaction with thyrotropin-releasing hormone

A superfusion technique was employed to study the release of [3H]dopamine from isolated bovine retina. Only K+-stimulated release was observed from both light- and dark-adapted retina; release by other stimuli was from dark-adapted retina only. Light-evoked release of [3H]dopamine from dark-adapted retina was blocked by thyrotropin-releasing hormone (TRH), which has previously been identified as a retinal neuropeptide. TRH itself released small amounts of [3H]dopamine from dark-adapted retina. These results are interpreted as indicating that TRH acts as a modulator of dopaminergic activity in retina through the agency of presynaptic autoreceptors. Evidence of the existence of a feedback inhibition system, probably mediated by dopaminergic autoreceptors, was found by the inclusion of sulpiride, a dopaminergic D2 receptor antagonist in the perfusate, which, in a stereoselective manner, enhanced spontaneous and light-evoked release of [3H]dopamine. On the other hand, dopamine (1 microM) reduced these effects. TRH did not affect the high-affinity uptake system for dopamine in retina; this, then, could not account for the effects on release. Radioligand binding showed a specific, saturable high-affinity binding system for [3H]TRH, with an apparent KD of 2.2 nM and a Bmax of 23 fmol/mg protein in bovine retinal membranes. Displacement experiments showed that specific [3H]TRH binding was displaced in the nanomolar range by spiperone and in the micromolar range by dopamine, whereas L-(--)-sulpiride was virtually inactive in displacing [3H]TRH.(ABSTRACT TRUNCATED AT 250 WORDS)

TRH receptor binding in retina and pituitary: major species variation

Retinas and anterior pituitary glands of nine readily available mammalian and one avian species have been examined for their TRH-sensitive binding of [3H]-[3-Me-His2]TRH. Among mammals, major species variations in TRH receptor binding have been detected in both tissues, amounting to about 100-fold in the retina and 20-fold in the pituitary. In the retina, TRH receptor binding was very high in the rat, quite high in sheep and guinea pig, intermediate in rabbit, pig, and mouse, and low but detectable in chicken, cat, calf and dog. In the pituitary gland, binding was very high in sheep, quite high in rabbit, rat, pig, calf and guinea pig, intermediate in chicken, and fairly low in mouse, cat, and dog. A number of possible interfering variables, including affinity differences, albino vs. non-albino strains, barbiturate anesthesia, time after death, sex and estrous cycle, age, and history of light exposure, were considered and/or tested directly, with generally negative results.