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The gene for subunit II of cytochrome oxidase is part of the mitochondrial genome. 17 beta-Estradiol, 1 nM, increased the levels of cytochrome oxidase II mRNA in the GH4C1 pituitary tumor cell line; the increases ranged from 3- to 16-fold over controls in different experiments. Insulin, 300 nM, estradiol, 1 nM, and epidermal growth factor, 10 nM, together caused a larger increase in cytochrome oxidase II mRNA accumulation than did estradiol alone. The dose-response relationship for the induction of cytochrome oxidase II mRNA by estradiol was similar to that for PRL mRNA; maximal induction occurred at about 10(-9) M. This concentration is 10-fold greater than that required for maximal stimulation of cell proliferation and of 1C28, another estrogen-inducible mRNA, indicating that the increase in cytochrome oxidase II mRNA is not a result of increasing the growth rate of the cells. The increase in cytochrome oxidase II mRNA was not caused by an increase in the number of copies of the cytochrome oxidase II gene. Estradiol therefore must induce in the mitochondria an increase in transcription or a decrease in degradation of cytochrome oxidase II mRNA.

To investigate the relationship of changes in cytosolic free calcium concentrations [( Ca2+]c) caused by TRH to changes in PRL secretion, we simultaneously monitored PRL release and [Ca2+]c, using the fluorescent Ca2+ indicator indo-1, in freshly isolated perifused cells from rat anterior pituitary glands. We found that a 30-sec pulse of 100 nM TRH triggered a transient spike of [Ca2+]c, but prolonged PRL release for up to 30 min; continuous administration of TRH caused a sustained elevation in [Ca2+]c, but the same pattern and amount of PRL release as that caused by the pulse of TRH. PRL secretion was refractory to further pulses of TRH given at 10-min intervals for 40 min, but did respond to a second pulse of TRH given 40 min after the first pulse with no intervening pulses. Pulses of TRH given every 10 min still triggered spikes of [Ca2+]c of the same magnitude as the first pulse, indicating that the cause of the refractory state must occur at a post-receptor step that is after the mobilization of [Ca2+]c. A 30-sec pulse of a high concentration of KCl caused a transient spike of [Ca2+]c and transient, not prolonged, release. Additional pulses of KCl cause progressively less PRL release, although the magnitude of the spikes in [Ca2+]c did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

To investigate whether dopaminergic reduction of PRL secretion is caused by an inhibition of release of Ca2+ from intracellular stores, we used a perifusion system to monitor simultaneously changes in intracellular Ca2+ concentrations ([Ca2+]c) and changes in PRL secretion from rat anterior pituitary cells, and from enriched populations of lactotrophs. We eliminated influx of extracellular Ca2+ by using medium with no added Ca2+ and 0.2 mM EGTA, conditions which abolished the increase in [Ca2+]c caused by 56 mM KCl. In this low Ca2+-containing medium, 100 nM TRH induced a burst of [Ca2+]c; the magnitude of the peak was the same whether the cells were perifused with low Ca2+-containing medium for 2 or 20 min before adding TRH, indicating the source of intracellular Ca2+ was stable under these conditions. After 2 min in this medium, TRH was still able to stimulate almost as much PRL release as in medium containing 1.8 mM Ca2+, and 1 microM dopamine inhibited this release, but did not affect the magnitude of the TRH-induced increase in [Ca2+]c. Preincubation for 5 min with dopamine did not affect the ability of a 30-sec incubation with TRH to stimulate the accumulation of inositol phosphate, inositol bisphosphate, and inositol trisphosphate, either in medium containing 1.8 mM Ca2+, or in low Ca2+-containing medium. Preincubation with dopamine for 5 min had no effect on TRH-induced mobilization of intracellular calcium. A source of Ca2+ is needed to refill internal Ca2+-stores discharged by TRH, and as dopamine lowered [Ca2+]c which might fill these stores, we tested to see if dopamine prevented.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel PTH-like peptide has recently been purified and cloned from human tumors associated with the syndrome of humoral hypercalcemia of malignancy. We surveyed the expression of mRNAs encoding this peptide in normal tissues by Northern analysis. One or more low abundance hybridizing transcripts was identified in poly(A)+ RNA prepared from human keratinocytes, thyroid, bone marrow, and fibroblasts, from bovine hypothalamus, pituitary, parathyroid, adrenal cortex, and adrenal medulla, and from rat brain, stomach mucosa, and fetal but not adult liver. One or more hybridizing transcripts was also identified in poly(A)+ RNA prepared from a number of established lines, including rat pituitary (GH4), rat pheochromocytoma (PC 12), human osteosarcoma (TE-85), and human medullary carcinoma (TT) cells. Northern analysis of mRNAs from abnormal human parathyroid tissue revealed an overexpression of transcripts for the PTH-like peptide which appeared to be specific for adenomatous or autonomous glands. These findings suggest that the PTH-like peptide is expressed in a number of endocrine and nonendocrine tissues, that it is developmentally expressed in at least one tissue (fetal liver), and that the regulation of its expression is abnormal in human parathyroid adenomas.