The stimulatory effect of beta-endorphin on the plasma prolactin levels was diminished in the rats treated with 6-hydroxydopamine

Intraventicular injection of beta-endorphin (beta LPH_61^?91) in urethane anesthetized male rats led to a dose dependent increase of plasma prolactin levels. Intravenous injection of apomorphine completely abolished the stimulatory effect of beta-endorphin. Animals treated with 6-hydroxydopamine (6-OHDA) and 6-OHDA plus desmethylimipramine showed inhibition of beta-endorphin induced prolactin release. These results suggest that beta-endorphin presynaptically inhibits the activity of dopaminergic neurones, leading to the stimulation of plasma prolactin levels.     

P2-purinergic receptors are coupled to two signal transduction systems leading to inhibition of cAMP generation and to production of inositol trisphosphate in rat hepatocytes

Stimulation of P2-purinergic receptors by ATP resulted in activation of phosphorylase, which was associated with marked production of inositol trisphosphate (Ins-P3), in rat hepatocytes. ATP also inhibited forskolin-induced accumulation of cAMP in the presence of a phosphodiesterase inhibitor. On the contrary, adenosine or AMP never inhibited the cAMP accumulation, but increased hepatocyte cAMP; the stimulation was antagonized by a methylxanthine. Thus, P1-purinergic receptors are linked to adenylate cyclase in a stimulatory fashion in hepatocytes. Various kinds of purine nucleotides stimulating P2-receptors can be divided into two groups on the basis of their relative abilities to stimulate Ins-P3 production and to inhibit cAMP accumulation; the first group including adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ADP, 5-adenylyl imidodiphosphate, GTP, and guanosine 5'-O-(3-thiotriphosphate) has an efficacy similar to that of ATP, and the second group of nucleotides including alpha, beta-methyleneadenosine 5'-triphosphate, beta, gamma-methyleneadenosine 5'-triphosphate (App(CH)2)p), and GDP exerts considerable inhibitory effects on cAMP accumulation, but only slight effects on inositol lipid metabolism. Treatment of hepatocytes with islet-activating protein, pertussis toxin, blocked the nucleotide-induced inhibition of cAMP accumulation, but exerted only a small effect on Ins-P3 production. In membranes prepared from hepatocytes, forskolin-stimulated adenylate cyclase was inhibited by GTP. This GTP-induced inhibition of the enzyme was susceptible to islet-activating protein and dependent on the concentration of ATP (or its derivatives, ATP gamma S or App(CH2)p). It is concluded that there are two types of P2-purinergic receptors: one is linked to adenylate cyclase via an inhibitory guanine nucleotide regulatory protein (Gi) and the other is linked to phospholipase C.     

A pertussis toxin-sensitive GTP-binding protein plays a role in the G0-G1 transition of rat hepatocytes following establishment in primary culture

Acute spontaneous c-myc gene expression and sustained increase of a GTP-binding protein(s) (G-protein) which is sensitive to islet-activating protein (IAP), pertussis toxin, occurred early during primary culture of adult rat hepatocytes. Following these earlier events, DNA synthesis was demonstrated in response to EGF and insulin. Addition of IAP immediately after plating of primary cultures inhibited c-myc expression and the hormone-induced DNA synthesis. Addition at 24 h or later following cell inoculation, however, produced only weak effects on DNA synthesis, even though the IAP-sensitive G-proteins were completely inactivated. We conclude that the IAP-sensitive G-protein(s) plays a role in the earlier process(es) of the G0-G1 transition, which is essential for the initiation of growth factor-dependent DNA synthesis.     

Effect of taurine on growth hormone and prolactin secretion in rats: possible interaction with opioid peptidergic system

The effect of taurine on growth hormone (GH) and prolactin (PRL) secretion was investigated in the urethane-alpha-chloralose anesthetized rats, considering the interaction with endogenous opioid peptidergic system. Intraventricular injection of taurine (0.25 and 1.0 mumol) stimulated GH and PRL secretion in a dose-dependent manner. However, 4.0 mumol taurine failed to show these effect. The intravenous infusion of naloxone (4 mg/kg b.w.) completely inhibited both the GH and PRL secretion induced by taurine (1.0 mumol). The combined treatment of taurine (1.0 mumol) and FK33-824 (Met-enkephalin derivative, 100 micrograms/kg b.w., i.v.) significantly increased GH and PRL responses induced by taurine or FK33-824 alone. These results indicate that taurine is an effective stimulator of GH and PRL secretion in rats, and that the mechanism of this action involves the opioid peptidergic system in the hypothalamus.     

Role of the early epithelium in the patterning of the teeth and Meckel's cartilage.

Embryonic epithelium from the mandibular branchial arch organizes the dentition and the deposition of Meckel's cartilage. During 9-11 days of gestation mandibular arch epithelium can induce teeth in nondental ectomesenchyme in both mice and birds. In addition, the deposition of Meckel's cartilage as a rod of cartilage in the middle of the first branchial arch is under the control of the epithelium. The epithelium inhibits chondrogenesis; if it is removed, large amorphous masses of cartilage are found instead of the narrow rod typical of Meckel's cartilage.     

Inheritance of dermatoglyphic configurations in the rat

Inheritance of dermatoglyphic configurations was studied on the palmar III interdigital pad of the rat (Rattus norvegicus). Four rats from each of the WKS and ACI/N inbred strains were mated with each other, and 54 F1 and 88 F2 hybrids were obtained. In addition, 52 offspring were produced by backcross mating between F1 hybrids and WKS and ACI/N parents. Whorls were the predominant pattern in the WKS strain and triradial patterns characterized the ACI/N strains. The F1 hybrids showed a wide range of pattern types, consisting of whorls, loops, cusps, arches, and triradial patterns. These patterns were intermediate in size between the two inbred strains. The F2 hybrids presented a distribution of patterns with a similar range as the F1, but the frequencies of some types were different. Patterns in the offspring of each backcross demonstrated a slight shift towards the characteristic pattern of the parental inbred strain. No sex difference was observed. Generally, the bilateral differences were striking, with a radial direction predominating on the left palm, and an ulnar one on the right palm, respectively. This study suggests that the dermal patterns are genetically determined, but also are influenced by environmental factors, especially in the hybrids.     

Collagenous substrata regulate the nature and distribution of glycosaminoglycans produced by differentiated cultures of mouse mammary epithelial cells

We have investigated the influence of culture substrata upon glycosaminoglycans produced in primary cultures of mouse mammary epithelial cells isolated from the glands of late pregnant mice. Three substrata have been used for experiments: tissue culture plastic, collagen (type I) gels attached to culture dishes, and collagen (type I) gels that have been floated in the culture medium after cell attachment. These latter gels contract significantly. Cells cultured on all three substrata produce hyaluronic acid, heparan sulfate, chondroitin sulfates and dermatan sulfate but the relative quantities accumulated and their distribution among cellular and extracellular compartments differ according to the nature of the culture substratum. Notably most of the glycosaminoglycans accumulated by cells on plastic are secreted into the culture medium, while cells on floating gels incorporate almost all their glycosaminoglycans into an extracellular matrix fraction. Cells on attached collagen gels secrete approx. 30% of their glycosaminoglycans and assemble most of the remainder into an extracellular matrix. Hyaluronic acid is produced in significant quantities by cells on plastic and attached gels but in relatively reduced quantity by cells on floating gels. In contrast, iduronyl-rich dermatan sulfate is accumulated by cells on floating gels, where it is primarily associated with the extracellular matrix fraction, but is proportionally reduced in cells on plastic and attached gels. The results are discussed in terms of polarized assembly of a morphologically distinct basal lamina, a process that occurs primarily when cells are on floating gels. In addition, as these cultures secrete certain milk proteins only when cultured on floating gels, we discuss the possibility that cell synthesized glycosaminoglycans and proteoglycans may play a role in the maintenance of a differentiated phenotype.