Locus coeruleus lesions decrease norepinephrine input into the medial preoptic area and medial basal hypothalamus and block the LH, FSH and prolactin preovulatory surge.

The aim of this work was to study the role of the dorsal noradrenergic ascending pathway (DNAP), which originates in the locus coeruleus (LC) on the preovulatory surge of luteinizing hormone (LH) follicle-stimulating hormone (FSH) and prolactin (PRL) by producing bilateral electrolytic lesions (cathodal or anodal) in this nucleus. LC lesions were placed at 11.00 h on proestrus in female rats with regular 4-day estrous cycles.

Interaction between norepinephrine and serotonin in the neuroendocrine control of growth hormone release in the rat.

Both alpha 2-adrenergic (alpha 2) and serotonergic (5HT) neurons are associated with stimulation of GH secretion via GRH release. The object of this study was to determine whether the 5HT system is involved in the stimulation of GH secretion by alpha 2-receptor agonists. There are two parts of this study.

The paradox of alpha 2 adrenergic regulation of prolactin (PRL) secretion. II. PRL-releasing action of the alpha 2 receptor antagonists.

It has been suggested that the stimulation of the secretion of PRL by the alpha 2 adrenergic receptor antagonists (yohimbine, piperoxane) results from blockade of an inhibitory influence imposed on PRL release by the central alpha 2 receptors (7, 15). Our present results do not support these conclusions for the following reasons: 1) The effectiveness of the alpha 2 receptor antagonists yohimbine (YOH), rauwolscine (RAU), Wy 26392 and idazoxan (IDAZ) respectively to activate secretion of PRL was not related to their alpha 2 antagonist potencies. RAU was more effective in activation of PRL secretion than either YOH or Wy 26392 although it had a similar alpha 2 antagonist activity, while IDAZ, the most potent alpha 2 blocker among the four compounds, did not stimulate PRL secretion.

The paradox of alpha 2 adrenergic regulation of prolactin (PRL) secretion. I. The PRL-releasing action of the alpha 2 receptor agonists.

Systemic (IV) administration of the alpha 2 receptor agonist clonidine is known to stimulate secretion of PRL and growth hormone (GH) suggesting a stimulatory role of the central alpha 2 receptors in the regulation of the two hormones. The present work confirms this notion for GH but indicates that the alpha 2 agonists stimulate PRL release by a peripheral action not involving central alpha 2 receptors. This conclusion is based on the following findings: 1) The minimum effective IV dose of clonidine or UK 14304 was four times larger for activation of PRL than GH secretion and had already manifest extracentral effects (elevation of arterial BP).

Evaluation and characterization of the hyt/hyt hypothyroid mouse. II. Abnormalities of TSH and the thyroid gland.

The hyt/hyt mouse (BALB/cBY-hyt, C.hytRF) provides a useful model for exploring the effect of inherited severe primary hypothyroidism. Studies were undertaken to try to define the basis of the primary hypothyroidism in mice homozygous for the autosomal recessive gene, hyt.