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Hepatic lipase (HL) gene expression was studied in rat ovaries. A transcript lacking exons 1 and 2 could be detected by reverse transcription-polymerase chain reaction (RT-PCR) in the ovaries of mature cyclic females and of immature rats treated with pregnant mare serum followed by human chorionic gonadotropin (hCG) to induce superovulation. By competitive RT-PCR the HL transcript was quantified. Low levels of HL mRNA were detected in ovaries of mature cyclic females and of immature rats. During superovulation HL mRNA was several fold higher than in mature cyclic rats and transiently increased to a maximum at 2 days after hCG treatment. Pulse-labelling of ovarian cells and ovarian slices with [35S]methionine followed by immunoprecipitation with polyclonal anti-HL IgGs showed de novo synthesis of a 47 kDa HL-related protein. Expression of the protein was transiently induced by gonadotropins with a peak at 2 days after hCG treatment. Induction of liver-type lipase activity occurred only after HL mRNA and synthesis of the HL-related protein had returned to pre-stimulatory levels. We conclude that in rat ovaries the HL gene is expressed into a variant mRNA and a 47 kDa protein. The expression of the HL gene in ovaries is inducible and precedes the expression of the mature, enzymatically active liver-type lipase.

Glucuronidation of iodothyronines in rat liver is catalyzed by at least three UDP-glucuronyltransferases (UGTs): bilirubin UGT, phenol UGT, and androsterone UGT. Bilirubin and phenol UGT activities are regulated by thyroid hormone, but the effect of thyroid status on hepatic glucuronidation of iodothyronines is unknown. We examined the effects of hypothyroidism induced by treatment of rats with propylthiouracil (PTU) or methimazole (MMI) or by thyroidectomy as well as the effects of T4-induced hyperthyroidism on the hepatic UGT activities for T4, T3, bilirubin, p-nitrophenol (PNP), and androsterone. Bilirubin UGT activity was increased in MMI- or PTU-induced hypothyroid and thyroidectomized rats, and decreased in hyperthyroid animals. T4 and, to a lesser extent, T3 UGT activities were increased in MMI- or PTU-induced hypothyroid rats, and T4 but not T3 glucuronidation also showed a significant increase in thyroidectomized rats. T4 but not T3 UGT activity was slightly decreased in hyperthyroid rats. While PNP UGT activity was decreased in thyroidectomized rats and increased in hyperthyroid animals, it was also markedly increased by MMI and slightly increased by PTU-induced hypothyroidism. In T4-substituted rats, MMI did not affect T4, T3, bilirubin and androsterone UGT activities but again strongly induced PNP UGT activity, indicating that this represented a direct induction of PNP UGT by the drug independent of its thyrostatic action. Androsterone UGT activity was hardly affected by thyroid status. Our results suggest a modest, negative control of the hepatic glucuronidation of thyroid hormone by thyroid status, which may be mediated by changes in bilirubin UGT activity. To our knowledge, this is the first report of the marked induction of a hepatic enzyme by MMI, which is not mediated by its thyroid hormone-lowering effect.

The human neuroblastoma cell line IMR32 produces and secretes substantial amounts of TRH-immunoreactivity (TRH-IR) as measured with radioimmunoassay (RIA) using the nonspecific antiserum 4319. It was found that synthesis of TRH-IR is dependent on neural differentiation: under serum-free conditions these cells exhibit neural characteristics as defined by morphological and biochemical standards. After culture for 2–5 days in serum-free medium cells grew large neural processes and expressed neuron-specific markers whereas glial-specific markers were absent. TRH-IR became detectable after 4–8 days serum-free conditions. Northern blot and chromatographic analysis, however, failed to detect proTRH mRNA and authentic TRH in these cells. Moreover, TRH-IR was undetectable in the RIA using TRH-specific antiserum 8880. TRH-IR produced by differentiated cells was retained on a QAE Sephadex A-25 anion-exchange column and thus negatively charged. HPLC analysis showed coelution with the synthetic peptide pGlu-Glu-ProNH2. Study of the mechanisms regulating production of this novel peptide in these cells should further elucidate the role differentation plays in the synthesis of neuropeptides.