M. Lis

Isolation of peptides with opiate activity from sheep and human pituitaries: Relationship to beta-lipotropin

Summary Human and ovine pituitaries were found to contain peptides of identical size, composition and N-terminal residue to the carboxy-terminal portion 61–91 of beta-lipotropin (1–91). These peptides exhibit morphine-line activity in the mouse vas deferens bioassay. Beta-lipotropins from both species where much lower potency than the new peptides in the same biossay. The findings favor the hypothesis that beta-lipotropin is the precursor of endogenous morphine-like peptides of pituitary origin.

Effects of thyrotropin-releasing hormone on behavioral and hormonal changes induced by β-endorphin

Abstract Adult male rats were injected intraventricularly either with saline or TRH (10 μg) 5 min prior to a second injection of either saline or β-endorphin (50 μg). The tripeptide produced a 100% increase of motility counts recorded over a 15 min period following the last injection, whereas β-endorphin decreased general motor activity. TRH pretreatment completely abolished the depressant effect of β-endorphin. In addition, TRH enhanced the PRL secretion induced by β-endorphin and antagonized the slight elevation of plasma GH levels observed in β-endorphin-treated rats. These results do not seem to be related to an interaction of TRH with opiate receptors since the tripeptide (10 −8 , 10 −6 M) added in vitro to rat brain homogenates did not alter the specific binding of 3 H-naloxone nor affect the displacement by β-endorphin of such binding.

β-endorphin induced akinesia in rats: Effect of apomorphine and α-methyl-p-tyrosine and related modifications of dopamine turnover in the basal ganglia

Abstract β-Endorphin (amino acid sequence 61–91 of β-lipotropin) administered intraventricularly at a dose of 13 n moles in rat induced akinesia and loss of corneal reflex. Apomorphine (20 mg/kg) which had been injected subcutaneously 20 minutes after the administration of β-endorphin fully reversed akinesia and elicited characteristic stereotyped behavior. During complete disappearance of akinesia, the corneal reflex was found to be still absent. Apomorphine (5 mg/kg) only partially reversed akinesia. Pretreatment with α-methyl-p-tyrosine (α-MT, 250 mg/kg) potentiated the effect of β-endorphin upon muscle rigidity. In a biochemical study, rats received β-endorphin (15 n moles) 60 minutes before sacrifice. Concentrations of dopamine (DA) and norepinephrine (NE) were not altered in any brain regions. A significant increase in concentrations of 5-hydroxytryptamine was obtained in the midbrain. In a DA and NE turnover study, rats received α-MT (250 mg/kg) 4 hours prior to β-endorphin and were sacrificed 60 minutes later. β-Endorphin partially corrected the decreased concentrations of DA induced by α-MT in the midbrain. A similar tendency toward correction of the decreased DA concentrations was observed in the striatum. The concentrations of NE decreased by α-MT in the midbrain, striatum and hypothalamus were not modified by β-endorphin

Lipotropin: Localization by radioimmunoassay of endorphin precursor in pituitary and brain☆

Abstract Beta-Lipotropic Hormone (LPH) was estimated in pituitary and brain by a radioimmunoassay specific for the N-terminal, non-opiate portion of the protein, and endorphin activity by an opiate radioreceptor assay. The intermediate pituitary is most concentrated in LPH and endorphin. Gel filtration indicated the presence in the pituitary of intact LPH and N-terminal fragments but only intact LPH in brain. Endorphin activity in pituitary is associated primarily with a component of 3000 daltons and to a lesser extent with one of about 2000 daltons. Brain endorphin activity is mostly accounted for by a 2000 dalton component, enkephalins representing an apparently minor activity. In pituitary and brain LPH and endorphin are entirely associated with a 12,000 g/10 min fraction.

Effects of Chronic Bromocriptine Treatment of an Estrone-Induced, Prolactin-Secreting Rat Pituitary Adenoma

Bromocriptine (BROM), a dopamine (DA) agonist, is commonly and successfully used for long-term treatment of human prolactinomas. We have studied the effects of chronic BROM administration to female 344 Fisher/Lis rats bearing an estrone-induced, prolactin (PRL)-secreting pituitary tumor recently characterized as a model for human prolactinoma. The animals were injected twice daily with BROM (2.5 mg/kg) or with diluent. After 1 month of treatment, the animals were sacrificed, and plasma collected and stored at -20 degrees C for PRL radioimmunoassay. The pituitary tumors were removed and tumoral mammotrophs dispersed enzymatically for studies of DA receptor binding and PRL release in vitro. BROM treatment significantly reduced tumor weight, cell size, rough endoplasmic reticulum, Golgi complexes and plasma PRL levels. [3H]-spiroperidol binding to tumoral mammotrophs was also evaluated. BROM induced a significant decrease in the number of DA binding sites without any changes in affinity. These results indicate that chronic BROM treatment of an animal model of prolactinoma induces tumor involution, reduction of PRL release and probably synthesis, and down regulation of dopaminergic binding sites.

Inhibition by beta-endorphin of dopamine-sensitive anenylate cyclase in rat striatum

Summary Beta-LPH 61–91 (beta-endorphin) inhibited the basal and dopamine-stimulated adenylate cyclase activity in a homogenate of rat striatum. Naloxone prevented this effect.

Estrone-induced, prolactin-secreting and dopamine-sensitive rat pituitary tumor

Prolactin (PRL)-secreting rat pituitary tumors were induced in female Fisher 344/Lis rats by s.c. implants of estrone (E1) pellets. Tumor growth was relatively fast and reached about 100 mg within 2 months. Ovariectomy at the time of E1 implants seemed to accelerate the growth of the tumors. Tumor cells in primary culture produced mainly PRL, while growth hormone (GH) release was about 2% of PRL production and the release of some other pituitary hormones did not exceed 1% of PRL values. Tumor cells were found to have high-affinity dopamine (DA) receptors. The addition of DA in vitro at 10(-10) M concentration stimulated PRL release, while at 10(-6) M concentration it inhibited the release of the hormone by more than 50% of control values. Histological, immunohistochemical and electron microscopical studies demonstrated the tumor to be composed mainly of maximally stimulated mammotrophs.

Solid-Phase Radioimmunoassay of Tonin in Extracts of Submandibular Glands of Rats Treated Chronically with Isoproterenol

Abstract Tonin, a proteolytic enzyme isolated from rat submandibular gland, can generate angiotensin II directly from angiotensin I, from angiotensin I-tetradecapeptide, and from angiotensinogen. A sensitive and specific solid-phase radioimmunoassay for measurement of tonin concentration and a method for measurement of tonin activity have been developed. Excellent correlation (coefficient r = 0.95) was found between the two methods. Tonin concentration and activity were studied in submandibular glands of rats chronically treated with isoproterenol. Almost complete depletion of tonin in rat submandibular gland was observed after 33 days of treatment. This observation was confirmed by polyacrylamide gel electrophoresis of homogenates of rat submandibular gland and immunocytochemistry. The immunocytochemical study revealed the presence of tonin in the cells of the granular convoluted tubules.

Fat Cell Adenylate Cyclase Activation by Sheep -Lipotropic Hormone

Summary Sheep β-LPH stimulated adenylate cyclase of isolated rat and rabbit adipose cells. Two doses of β-LPH were compared with two lipolytically equipotent doses of synthetic ACTH. ACTH was found to be more active in stimulating adenylate cyclase of rat fat cells while β-LPH was more potent in rabbit cells. β-LPH activation of adenylate cyclase was blocked when EGTA was added to the incubations. Differences in adenylate cyclase system in rats and rabbits were also observed.

Beta-endorphin and beta-lipotropin secretion by an acth- -secreting mouse pituitary tumor.

The discovery of the morphine-like peptide, betaendorphin, which is identical to the sequence 61-91 of beta-lipotropin (beta-LPH) [l-4] gave additional support to the idea that beta-LPH is a prohormone as suggested [5-71. In vitro biosynthetic experiments have demonstrated the production by pituitary tissue of betaendorphin, beta-LPH, and gamma-LPH (betaLPH l-58) [8-lo]. It has been also suggested that an ACTHsecreting mouse pituitary tumor cell line (AtT-20/D-16V) synthesizes beta-LPH as a part of a larger precursor protein which contains the sequence of ACTH [ 1 l-l 31. We demonstrate here the existence of immunoreactive betaendorphin in the plasma of AtT-20 tumor-bearing mice and in extracts of these tumors.