Temporal requirement for epidermal growth factor and insulin in the stimulation of hepatocyte DNA synthesis

Primary monolayer cultures of adult rat hepatocytes were used to study the temporal interaction of epidermal growth factor (EGF) and insulin in their stimulation of DNA synthesis. The hepatocytes were cultured both under defined conditions and with serum. EGF and insulin interacted synergistically. The entry into S phase (G1 exit) followed first-order kinetics both in untreated and hormone-stimulated cells. Addition of EGF and insulin at the time of plating did not alter the lag period before the DNA synthesis started (25-26 h), but the rate constant for the S phase entry increased five- to sixfold. Experiments where the time of hormone addition was varied indicated that insulin exerted its strongest effect at the time of plating, whereas the cells became more responsive to EGF after being cultured for up to 40-50 h. The responsiveness to EGF at these later stages required an early exposure of the hepatocytes to insulin. When the administration of EGF to insulin-pretreated hepatocytes was postponed for 44 h after plating in serum-free medium, the cellular sensitivity was increased as compared to EGF treatment at 0 h (a one-log shift of the dose-effect curve), the rate of S phase entry was more rapid, and the lag period for the onset of the EGF effect (i.e., shift of rate constant) was shortened (6-7 h vs. 26 h).     

Bidirectional concentration-dependent effects of glucagon and dibutyryl cyclic AMP on DNA synthesis in cultured adult rat hepatocytes

Glucagon and dibutyryl cyclic AMP exerted both stimulatory and inhibitory effects on hepatocyte DNA synthesis when added to primary monolayer cultures in the presence of serum, dexamethasone, insulin and epidermal growth factor. The stimulation occurred at low concentrations of glucagon (1 pM-1 nM) or dibutyryl cyclic AMP (1 nM-1 microM), while the agents inhibited DNA synthesis at higher concentrations (usually glucagon at over 10 nM or dibutyryl cyclic AMP at over 10 microM). The stimulatory effect was stronger at low cell densities (less than 20 X 10(3) hepatocytes/cm2). When the hepatocytes were cultured at higher densities, stimulatory effects were reduced or absent and the inhibition of (hormone-induced) DNA synthesis by a high concentration of glucagon was much more pronounced than at low cell densities. These results indicate dual, bidirectional, effects of cyclic AMP on hepatocyte DNA synthesis.     

The Measurement of Spinal Cord Tissue pH Using a Diffusible, Lipid-Soluble, pH-Sensitive Fluorescent Indicator

Abstract: Spinal cord tissue pH was measured in cats at normocapnia, hypocapnia, hypercapnia and death from anoxia using a pH-sensitive fluorescent indicator (umbelliferone) with both molecular and ionic fluorophors. A ratio analysis of the indicator's calibrated 450 nm fluorescent tissue clearance curves from 340 and 370 nm excitation permitted direct in vivo tissue pH determinations. Fifteen animals were divided into three equal groups according to different arterial carbon dioxide tensions (P_a co₂):five animals at P_a co₂ 20, five animals P_a co₂ 40 and five animals P_a co₂ 60 torr. Spinal cord tissue pH varied linearly with arterial pH, but within narrower limits. These values (arterial versus cord pH) were: 7.46 versus 7.15; 7.21, 7.09; and 7.04, 7.00. At death from hypoxemia the arterial pH fell to 6.99 and spinal cord to 6.67. The clearance curves of umbelliferone in spinal cord varied according to P_a co₂ and appeared to reflect spinal cord blood flow.     

Gut evacuation rates and ingestion rates of Eudiaptomus graciloides measured by means of the gut fluorescence method

Journal of Plankton Research, 8, 973–983, 1986 FIg. 2. Time-dependent changes in the gut content (percentageof initial ng pigment) of E. gro.ciloides at different temperaturesunder simultaneous feeding. Fig. 4. The relationship between instantaneous evacuation rateand temperature of E. graciloides. The regresston equation forfeeding animals: y = 0.0044 e(0.141 ) (r² = 0.90). For comparisonthe results of non-feeding animals are indicated with open circles.     

Rapid constitutive internalization and externalization of epidermal growth factor receptors in isolated rat hepatocytes. Monensin inhibits receptor externalization and reduces the capacity for continued endocytosis of epidermal growth factor

It was previously demonstrated that freshly isolated rat hepatocytes can internalize severalfold more epidermal growth factor (EGF) molecules than the number of surface EGF receptors, suggesting extensive reutilization of receptors during endocytosis (Gladhaug, I. P. & Christoffersen, T. (1987) Eur. J. Biochem. 164, 267-275). The present report attempts to explore the pathways involved in the externalization of EGF receptors. Incubation of hepatocytes at 37 degrees C in the absence of ligand increased the surface receptor pool by 50-100% within 45 min. Pretreatment with monensin inhibited the turnover of the surface EGF receptor pool by 50-60% within 10 min and blocked the temperature-dependent externalization of receptors. Cycloheximide caused a slower attenuation of the surface receptor pool, whereas tunicamycin and chloroquine did not significantly affect the exchange of receptor pools. Monensin reduced the surface receptor pool and the endocytic uptake in corresponding proportions, without affecting the internalization of prebound EGF. Endocytic uptake was unaffected by chloroquine and slightly reduced by cycloheximide. The internalization of unoccupied receptors and the endocytosis of prebound EGF followed similar kinetics (t1/2 approximately 5 min), suggesting that unoccupied receptors are internalized at a rate comparable to that of occupied receptors. The results suggest that there is a rapid turnover of the surface pool of EGF receptors with constitutive internalization of unoccupied surface receptors and externalization of internal receptors. This is consistent with, but does not prove, a true recycling of the EGF receptors in the hepatocytes. The monensin-sensitive externalization pathway determines the capacity for continued endocytosis of EGF.     

Pertussis toxin abolishes the inhibitory effects of prostaglandins E1, E2, I2 and F2 alpha on hormone-induced cAMP accumulation in cultured hepatocytes

Several prostaglandins inhibit the cAMP response to glucagon and beta-adrenergic stimulation in hepatocytes. To probe the mechanism of this inhibition, we have examined in primary hepatocyte cultures how pretreatment with pertussis toxin (islet-activating protein) influences the ability of the cells to respond to hormones and prostaglandins. Pertussis toxin augmented the effects of glucagon, epinephrine and isoproterenol, and also markedly enhanced the cAMP response to prostaglandin E1 (PGE1). Furthermore, whereas PGE1, PGE2, PGI2 and PGF2 alpha attenuated the cAMP responses to glucagon in control cultures, this inhibition was abolished in cells pretreated with pertussis toxin. A more detailed comparison was made of the effects of PGE1 and PGF2 alpha. In cells not treated with pertussis toxin, both these prostaglandins at high concentrations reduced the cAMP response to glucagon and isoproterenol by approximately 50%, but dose-effect curves showed that PGE1 was about 100-fold more potent as an inhibitor than PGF2 alpha. Pertussis toxin abolished the inhibitory effects of PGE1 and PGF2 alpha with almost identical time and dose requirements. The results obtained with PGE1, PGE2, PGI2 and PGF2 alpha suggest that prostaglandins of different series attenuate hormone-activable adenylate cyclase in hepatocytes through a common mechanism, dependent on the inhibitory GTP-binding protein.     

A new superfamily classification of the Caridea (Crustacea: Pleocyemata) based on phylogenetic pattern

Present groupings of Caridea are notoriously unsatisfactory at the superfamily level. Principles of phylogenetic systematics are used to reconstruct 14 monophyletic subgroups of Caridea, based on 19 synaomorphies of adults. The following sequenced phylogenetic classification is provided (main diagnostic character for each superfamily within brackets): 1. Atyoidea (distal lash of Mxp, reduced); Oplophoridae; Atyidae; Pasiphaidae; Agostocarididae; Alvinocarididae; Bresiliidae; Psalidopodidae; Disciadidae; 2. Stylodactyloidea (mandibular palp with 2 segments or absent); Stylodactylidea; Campylonotidae; 3. Eugonatonotoidea (abdominal somite III with dorsal carina bifurcate); Eugonatonotidae; 4. Palaemonoidea (basal segment of antennular peduncle with distolateral tooth); Rhynchocinetidae; Palaemonidae; 5. Nematocarcinoidea (ventral lobe of scaphognathite narrowly triangular); Nematocarcinidae; 6. Pandaloidea (P₁ with chela microscoic or absent); Pandalidae; “Plesionikidae”; Heterocarpidae; Heterocarpoididae; Dorodoteidae; Thalassocarididae; Physetocarididae; 7. Crangonoidea (incisor process of mandible absent); Barbouriidae; Lysmatidae; Merguiidae, fam. n.; Processidae; Glyphocrangonidae; Crangonidae; 8. Alpheoidea (carpus of P₂ with less than 17 segments); Merhippolytidae, fam. n.; Nauticarididae; Alopidae; Bythocarididae; Thoridae; Hippolytidae; Pterocarididae, fam. n.; Ogyrididae; Alpheidae. The monotypic hippolytid taxon Thorellinae, subfam. n., has been formally diagnosed. A survey of the lower Caridea has furnished 276 enera and 2418 species and subspecies. The new superfamily system is simpler, genealogically informative and more precisely diagnosed than previous schemes. These have failed as general reference systems because they were based on the wrong premises that similarities indicate phylogenetic relationships or can be used to construct a single acceptable hierarchy.     

A simple medium for the study of hepatocyte growth in culture under defined conditions

Summary The combination (1∶1) of Dulbecco's modified Eagle's medium and Waymouth's medium MAB 87/3 was found to provide favorable conditions for serum-free culture and growth of adult rat hepatocytes. In this simple medium, a majority of hepatocytes stimulated by epidermal growth factor plus insulin entered S phase and divided, with a normal (13 h) interval between DNA synthesis and cell division. The proliferative response did not require extra substratum or the presence of serum, even during cell isolation and plating. This work was supported by the Norwegian Cancer Society.