Molecular evolution of the domain structures of protein disulfide isomerases

Protein disulfide isomerase (PDI) is an enzyme that promotes protein folding by catalyzing disulfide bridge isomerization. PDI and its relatives form a diverse protein family whose members are characterized by thioredoxin-like (TX) domains in the primary structures. The family was classified into four classes by the number and the relative positions of the TX domains. To investigate the evolution of the domain structures, we aligned the amino acid sequences of the TX domains, and the molecular phylogeny was examined by the NJ and ML methods. We found that all of the current members of the PDI family have evolved from an ancestral enzyme, which has two TX domains in the primary structure. The diverse domain structures of the members have been generated through domain duplications and deletions.

Molecular phylogeny of zooxanthellate bivalves

The aim of this research was to analyze the phylogenetic relationships of zooxanthellate bivalves belonging to the genera Tridacna, Hippopus, Fragum, and Corculum as well as to the closely related azooxanthellate bivalves belonging to Vasticardium and Fulvia. The small-subunit ribosomal RNA genes (18S rDNAs) from these bivalves were amplified by polymerase chain reaction with universal eukaryotic primers and were then sequenced. The sequence data from each species were analyzed by the neighbor-joining, maximum parsimony, and maximum likelihood methods, and phylogenetic trees were constructed. The results were essentially consistent with the morphological taxonomy of these bivalves. Thus, the zooxanthellate clams branch into two lineages, one composed of the genera Fragum and Corculum in the family Cardiidae, and the other composed of the genera Tridacna and Hippopus in the family Tridacnidae. However, present results indicate that the azooxanthellate clams analyzed (Vasticardium flavum and Fulvia mutica) are more likely to form a clade with the species of Tridacna and Hippopus than with those of Fragum and Corculum. This topology suggests that either the symbiosis with zooxanthellae occurred independently in each of two lineages, Tridacna-Hippopus and Corculum-Fragum, or the symbiosis was established in clams ancestral to the lineages of both the zooxanthellate clams and the azooxanthellate clams Vasticardium and Fulvia, and the latter lost the symbiotic relationship after the symbiotic clam lineages had diverged.

Molecular cloning and characterization of the gene encoding N'-[(5'-phosphoribosyl)-formimino]-5-aminoimidazole-4-carboxamide ribonucleotide (BBM II) isomerase from Arabidopsis thaliana

We have isolated an Arabidopsis BBM II isomerase cDNA from an Arabidopsis cDNA library, by means of functional complementation of the E. coli hisA mutant strain HfrG6. The isolated cDNA encodes a polypeptide of 304 amino acids with a calculated molecular weight of 33,363. Sequence comparison with the HIS6 proteins of yeasts revealed that Arabidopsis BBM II isomerase contains an N-terminal extension of approximately 40 amino acids that shows the general properties of chloroplast transit peptides. This finding is consistent with the localization of other histidine biosynthetic enzymes, such as imidazoleglycerolphosphate dehydratase and histidinol dehydrogenase, in the chloroplasts in higher plants. The primary structure of the mature protein was 50% and 42% identical, respectively, to the HIS6 proteins of Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively, while no prominent sequence similarity to the bacterial BBM II isomerase was found. That the isolated Arabidopsis cDNA actually encodes a functionally active BBM II isomerase activity was confirmed in an in vitro enzyme assay using a crude extract prepared from strain HfrG6 transformed with the Arabidopsis BBM II isomerase cDNA.

Nucleotide sequence of plasmid pAQ1 of marine cyanobacterium Synechococcus sp. PCC7002

We have determined the complete nucleotide sequence of pAQ1, the smallest plasmid of the unicellular marine cyanobacterium Synechococcus sp. PCC7002. The plasmid consists of 4,809 bp and has at least four open reading frames that potentially encode polypeptides of 50 or more amino acids. We found that a palindromic element, the core sequence of which is G(G/A)CGATCGCC, is over-represented not only in plasmid pAQ1 but also in the accumulated cyanobacterial genomic sequences from Synechococcus sp. PCC6301, PCC7002, PCC7942, vulcanus and Synechocystis sp. PCC6803 within GenBank and EMBL databases. It suggests that this sequence might mediate gene rearrangement, thus increasing genetic diversity, since recombination events are frequent in cyanobacteria.

Inhibitory effect of central dopamine on basal pancreatic secretion in conscious rats

We examined the role and the peripheral mechanism of action of central dopamine on basal pancreatic exocrine secretion in conscious rats. Rats were fitted with bile and pancreatic catheters to collect bile and pancreatic juice separately and also with a left lateral brain ventricle and external jugular vein catheters. After 90-min basal collection, the D1- and D2-receptor antagonists (Sch-23390 and eticlopride, respectively) and dopamine were administered into the lateral brain ventricle. Sch-23390 (30, 100, and 300 nmol/rat), but not eticlopride (300 nmol/rat), stimulated pancreatic fluid and protein secretion. Dopamine (30, 100, and 300 nmol/rat) inhibited pancreatic secretion lose dependently. Pretreatment with Sch-23390 prevented the inhibitory effect of dopamine. Intravenously injected Sch-23390 or dopamine had no effect on pancreatic secretion. The inhibitory effect of dopamine was blocked by bretylium, an inhibitor of norepinephrine release, and phentolamine, an alpha-blocker, but not by vagotomy. The beta-antagonist propranolol alone significantly inhibited basal pancreatic secretion, and dopamine did not modify the inhibitory effect of propranolol. The proton pump inhibitor omeprazole partially but not completely reduced the inhibition by dopamine. These results suggest that central dopamine inhibits pancreatic exocrine secretion via D1-like receptors and that the inhibitory effect is mediated via sympathetic nerves, especially alpha-adrenoceptors.

Molecular evolution of the photolyase-blue-light photoreceptor family

The photolyase-blue-light photoreceptor family is composed of cyclobutane pyrimidine dimer (CPD) photolyases, (6-4) photolyases, and blue-light photoreceptors. CPD photolyase and (6-4) photolyase are involved in photoreactivation for CPD and (6-4) photoproducts, respectively. CPD photolyase is classified into two subclasses, class I and II, based on amino acid sequence similarity. Blue-light photoreceptors are essential light detectors for the early development of plants. The amino acid sequence of the receptor is similar to those of the photolyases, although the receptor does not show the activity of photoreactivation. To investigate the functional divergence of the family, the amino acid sequences of the proteins were aligned. The alignment suggested that the recognition mechanisms of the cofactors and the substrate of class I CPD photolyases (class I photolyases) are different from those of class II CPD photolyases (class II photolyases). We reconstructed the phylogenetic trees based on the alignment by the NJ method and the ML method. The phylogenetic analysis suggested that the ancestral gene of the family had encoded CPD photolyase and that the gene duplication of the ancestral proteins had occurred at least eight times before the divergence between eubacteria and eukaryotes.

Alpha- and beta-subunits of a V-type membrane ATPase in a hyperthermophilic sulfur-dependent archaeum, Thermococcus sp. KI

The genes encoding alpha- and beta-subunits of a V-type ATPase in a sulfur-dependent hyperthermophilic archaeum, Thermococcus sp. KI, were cloned and sequenced. The deduced amino acid sequences were approximately 60, 50 and 25% identical to those of other archaeal, eukaryotic V-type and E. coli F-type ATPase, respectively. Phylogenetic analysis revealed that Thermococcus ATPase was closely related to that of Thermus, and those of Methanosarcina and Halobacterium.

Endoscopic transvesico-transurethral approach for repair of vesicovaginal fistula: initial case report

Through an endoscopic transvesico-transurethral approach, we closed a vesicovaginal fistula that occurred after hysterectomy in a patient with uterine leiomyoma. The 3-mm fistula, located in the midportion of retrotrigone, was resected transurethrally and sutured in two layers through two 5-mm suprapubic trocars placed into the bladder and the urethral route under pneumobladder. The patient had no urine leakage from the vagina after surgery.

Presence of a novel hamster oral papillomavirus in dysplastic lesions of hamster lingual mucosa induced by application of dimethylbenzanthracene and excisional wounding: molecular cloning and complete nucleotide sequence

A combination of 9,10-dimethyl-1,2-benzanthracene (DMBA) application and excisional wounding on the lingual tips of Syrian Golden hamsters (Mesocricetus auratus) induces dysplastic and malignant mucosal lesions. Papillomavirus genus-specific antigen and viral particles, measuring 55 nm in diameter, were demonstrated in the nuclei of squamous cells of dysplastic lesions showing koilocytotic change. In this study, we cloned a circular genome at a single Kpnl site from one of these dysplastic lesions. The genomic sequence of this clone, consisting of 7647 bp, was shown to be that of a novel papillomavirus with a conserved genomic organization. We named the new virus hamster oral papillomavirus (HOPV). All dysplastic lesions induced by this combination of DMBA application and excisional wounding contained viral DNA. Although Southern blot hybridization analysis could not detect the HOPV genome, PCR analysis demonstrated the latent HOPV genome in the tongue and skin of an untreated hamster. These results suggest that latently present HOPV genome is reactivated by the DMBA/wounding procedures. Lingual HOPV infection may be an important model for gaining insight into the interactions between papillomavirus infection, chemical carcinogens and physical irritations in carcinogenesis or malignant transformation.

Involvement of cholinergic processes in cholecystokinin (CCK) release [corrected] by luminal oleic acid

Cholecystokinin (CCK) is an important bioactive peptide that stimulates pancreatic enzyme secretion. Circulating CCK is secreted from endocrine cells in the upper small intestine in response to various luminal stimuli and to vascular administration of gastrin releasing peptides. However, the mechanism of its release has not been fully elucidated. In the present study, the vascularly perfused duodenojejunum was isolated from male Wistar rats. The effects of luminal infusion of sodium oleate (2 or 0.4%) or intra-arterial infusion of neuromedin C(10(-7) M) with or without atropine and with a recently synthesized specific bombesin antagonist (EABI) were examined. The CCK release produced by intra-arterial infusion of neuromedin C was inhibited by EABI in a dose-dependent manner. The CCK release produced by luminal sodium oleate was inhibited by atropine, but not affected by EABI. The CCK release stimulated by luminal sodium oleate is mediated, at least in part, by a cholinergic mechanism, but neuromedin C directly stimulates CCK release via its receptor on CCK-producing cells.

Central somatostatin prevents vagal efferent nerve excitation produced by TRH but not by 2-deoxy-D-glucose

Thyrotropin-releasing hormone (TRH) administered intracerebroventricularly and intravenous injection of 2-deoxy-D-glucose (2-DG) stimulate pancreatic exocrine secretion via vagal efferent nerve excitation. We examined whether centrally administered somatostatin would inhibit pancreatic exocrine secretion that was stimulated by vagal efferent nerve excitation in conscious rats. The animals were prepared with cannulas draining bile and pancreatic juice separately and with a duodenal cannula, a cerebroventricular cannula, and a right jugular vein cannula. Intracerebroventricular injection of somatostatin (0.4 or 4 nmol) significantly inhibited pancreatic secretion induced by TRH (50 or 500 pmol) in a dose-dependent manner. Intravenous injection of somatostatin had no effect on pancreatic secretion stimulated by TRH. On the other hand, somatostatin injected centrally did not affect pancreatic secretion induced by 2-DG (75 mg/kg) or basal secretion. These results suggest that TRH and 2-DG stimulate vagal efferent nerves via distinct mechanisms and that central somatostatin selectively inhibits excitation of the vagus induced by peptidergic (TRH) stimulation.

Efficacy of toki-shigyakuka-gosyuyu-syokyo-to (danggui-sini-jia-wuzhuyu-shengjiang-tang) on peripheral circulation in autonomic disorders

To investigate the improvement in peripheral circulation in autonomic disorders, we monitored skin temperature in the tails of rats by thermography before and after the oral administration of boiled water extract of Toki-shigyakuka-gosyuyu-syokyo-to (TSGS-to). Oral administration of this extract elevated the temperature, calculated as the calories of radiant heat in the rat tail 5-10 min after uptake. The temperature elevation remained stable for more than 20 min. Calories were significantly reduced 60 min after uptake and almost returned to initial values 90 min later. Some of the constituent herbs, especially Angelicae radix, Cinnamomi cortex, Evodiae fructus, and Zingiberis rhizoma, appeared to be active in relieving hypothermia.

Aging impairs release of central and peripheral cholecystokinin (CCK) in male but not in female rats

BACKGROUND

Cholecystokinin (CCK) is an important bioactive peptide which stimulates pancreatic enzyme secretion and is also a neuromodulator in the central nervous system. We examined whether CCK release from the central and peripheral tissues was decreased in old animals, and whether there were sex-related differences.

METHODS

Young (5-10-month-old) and old (25-29-month-old) male and female Wistar rats were used. Synaptosomes were prepared from the cerebral cortex, and the vascularly perfused duodenojejunum was isolated to examine central and peripheral CCK release, respectively. In some young female rats, 21 days after bilateral ovariectomy, the peripheral CCK release and the changes in CCK mRNA levels were examined.

RESULTS

The central CCK release was impaired in response to the higher concentration of KCl, and the peripheral CCK response to the highest dose of neuromedin C was impaired in old male rats. However, no aging effect was observed in female rats, and ovariectomy did not affect CCK release or CCK mRNA level.

CONCLUSIONS

CCK release from both central and peripheral tissues was decreased in old male rats, but not in old female rats.

[Age-related alteration of inhibitory effects of isradipine on alpha 1-adrenoceptor mediated responses]

We studied age-related alteration of inhibitory effects of a Ca2+ channel antagonist, isradipine, on alpha 1-adrenoceptor mediated responses in 6-, 10-, and 40-week-old rats. Age-related changes were observed in the inhibitory effects of isradipine on the norepinephrine-induced maximum contractions in the isolated thoracic aorta, the amplitude of the Ca(2+)-evoked increase of intracellular Ca2+ concentration and sustained contraction in fura-2-loaded preparations and the maximum number of binding sites (Bmax) of [3H] (+)-isradipine to aortic membranes. The dissociation constant (KD) of [3H] (+)-isradipine did not alter with age. In anesthetized rats, isradipine inhibited the dose-response curves of norepinephrine on the blood pressure in 6- and 40-week-old animals more effectively than those in 10-week-old animals. An inverse relationship between the potency of norepinephrine in the isolated thoracic aorta, the inhibitory effects of isradipine on the norepinephrine-induced maximum contractions and the logarithm of Bmax obtained in the [3H] (+)-isradipine binding experiment were found. These results suggest that the age-related alteration of inhibitory effects of isradipine on alpha 1-adrenoceptor mediated contractile responses and the increase of blood pressure are due to changes in the alpha 1-adrenoceptor density and the population of voltage-dependent L-type Ca2+ channels, rather than changes in the affinity of drug to the alpha 1-adrenoceptor or Ca(2+)-sensitivity of contractile elements of aortic smooth muscle.

Long term treatment with (-)deprenyl reduces the optimal dose as well as the effective dose range for increasing antioxidant enzyme activities in old mouse brain

C57BL mice of the male sex received different doses of (-)deprenyl (0.25, 0.5, 1.0 mg/kg per injection 3 times a week, s.c.) for 3 months beginning at the age of 26 months. At the age of 29 months, animals were sacrificed and superoxide dismutase (SOD) and catalase (CAT) activities were examined in several brain regions. The dose of 0.5 mg/kg (3 times a week) was most effective in increasing SOD and CAT activities in S. nigra, striatum and cerebral cortex but not in hippocampus or cerebellum. The dose of 0.25 mg/kg was also effective in increasing enzyme activities, but the effect was much lower than the dose of 0.5 mg/kg. The magnitudes of increase in enzyme activities with the dose of 0.5 mg/kg, however, were generally much lower than respective values we previously found in animals treated with (-)deprenyl for only 3 weeks. The highest dose of 1.0 mg/kg had negligible effect. Enzyme activities in all groups of animals that were examined 2 weeks after the last (-)deprenyl dose were practically the same as respective control values. Together with the results from our previous study with short term (-)deprenyl treatment in old mice, these results replicate our previous findings in old female rats. We showed that longer term treatment with (-)deprenyl reduces the optimal dose for increasing antioxidant enzyme activities by a factor of 5 to 10. The present study further indicates that longer term treatment with (-)deprenyl also reduces the effective dose range of (-)deprenyl as well as the magnitude of increase of enzyme activities. If the effect of (-)deprenyl for increasing these antioxidant enzyme activities in selective brain regions is causally related to its effect of increasing average life expectancies of animals, the selection of a proper dose of the drug may be a critical factor for life span studies in which the drug, is administered for more than one year.

An improved quantitative RT-PCR fluorescent method for analysis of gene transcripts in the STS-65 space shuttle experiment

We describe a reverse transcription polymerase chain reaction (RT-PCR) technique using fluorescent dUTP to examine changes in mRNA level in samples. In this procedure, the amplified product is identified by the fluorescent detection system in an automated DNA sequencer, and if the MW of the DNA/RNA or the fluorescent dye is different, several samples can be analyzed in a single lane. The basis for this technique is similar to that of radiolabeled methods, and we applied this technique for the comparison of the expression level of the rat c-myc gene in osteoblasts exposed to microgravity and unit gravity conditions. Using the fluorescent- and radiolabeled methods, the level of rat c-myc mRNA were compared quantitatively and the results demonstrated that the c-myc expression level was not altered by microgravity. Therefore, this fluorescent RT-PCR technique is useful for gene expression analysis particularly when the samples are limited, such as in space flight experiments. The method also allows for rapid assessment of mRNA changes in many samples simultaneously.

Upregulation of antioxidant enzyme activities by deprenyl. Implications for life span extension

In order to elucidate the exact role of antioxidant enzyme activities such as superoxide dismutase (SOD) in the aging process of animals, we compared various enzyme activities in different brain regions and in the liver of young (6-8 mo) and old (28-30 mo) Fischer-344 (F-344) rats. While Mn-SOD activities were elevated 3-5-fold in specific brain regions such as hippocampus, striatum and substantia nigra in brains of old male rats compared with the young, in females both forms of SOD (Cu, Zn- and Mn-) enzyme activities remained essentially unchanged with aging. Continued subcutaneous infusion of deprenyl for 3 weeks caused a 2-3-fold increase in activities of both Cu Zn- and Mn-SOD and a 50-60% increase in CAT activities in striatum and substantia nigra but not in hippocampus, cerebellum or the liver. Further, long-term treatment of old male rats with deprenyl caused a significant increase in the remaining life expectancy from 24 months of age by 34%. In conclusion, activities of antioxidant enzymes in these regions examined do not show any uniform age-associated change, suggesting that changes in these enzyme activities do not have any specific role in the life span of rodents in general terms. In contrast, the results of our deprenyl study suggests the possibility that the protection of catecholaminergic neurons by an upregulation of SOD and CAT activities plays a significant role in the life span of animals.

Leupeptin causes an accumulation of lipofuscin-like substances and other signs of aging in kidneys of young rats: further evidence for the protease inhibitor model of aging

The "protease inhibitor model of aging" has been proposed on the basis of observations that young rat brains, livers, and retinas exposed to a protease inhibitor, leupeptin, accumulate lipofuscin-like substances (LLS) that are similar to age pigment, and also display a variety of other manifestations of aging. In order to validate this hypothesis in more general terms, the present study reports attempts to induce age-like changes in kidney cells of young rats. Male F-344 rats (4-5 weeks of age) were continuously infused intraperitoneally (i.p.) with various doses of leupeptin (1-50 mg/100 g/day) for 2 weeks. Control animals received saline solution and normal aged rats (27-30 months-old) received no treatment. Animals were sacrificed and subjected to histological examination. In kidneys of leupeptin-, but not saline-treated rats, generally round-shaped PAS-positive particles were clearly observed, which were predominantly distributed in proximal convoluted tubules, and which resembled particles in normal aged kidneys. With increasing drug doses, particles tended to become bigger and more numerous. The dominant accumulation of LLS in cells of the proximal convoluted tubules had a fine morphologic configuration that resembled age pigments in old rats. Also, there was a concomitant thickening of the basement membrane that was present in leupeptin-treated and aged kidneys, but not in controls. The results, therefore, support the protease inhibitor model of aging and provide an experimental tool for probing the cellular mechanisms of aging.

Role of cholecystokinin (CCK)-A receptor for pancreatic growth after weaning: a study in a new rat model without gene expression of the CCK-A receptor

This work extends a recent observation that Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which have been established as an animal model of non-insulin-dependent diabetes mellitus, show no expression of the cholecystokinin (CCK)-A receptor gene in the pancreas. The CCK-A receptor is known to be involved in regulating pancreatic exocrine function and growth. We examined the growth of the pancreas in terms of wet weight, enzyme compositions, and protein and DNA contents at 5-6 and 24-25 weeks of age in OLETF rats and control (Long-Evans Tokushima; LETO) rats. The pancreatic wet weight increased significantly with age in both OLETF and LETO rats but was significantly lower in OLETF rats than in LETO rats. The total DNA contents in the whole pancreas (cell numbers) were comparable for both strains and increased significantly with age. However, the ratio of protein content to DNA content (the cell size) significantly increased with age in LETO rats, with no increase in OLETF rats. The changes in chymotrypsin, amylase, and insulin with respect to age were in the same direction in both strains: a decrease or no change in total and/or cellular contents of chymotrypsin and insulin and increases in amylase. These results suggest that the CCK-A receptor plays some role in the increase in cell size associated with normal growth of the pancreas from 5 to 25 weeks of age (after weaning).

Effects of pancreatic duct ligation and aging on acute taurocholate-induced pancreatitis. Experiments in the perfused pancreas in rats

CONCLUSION

When taurocholate was injected into the common bile duct, high ductal pressure due to ligation of the pancreatic duct did not produce more damage in the pancreas of both old rats and young adult rats, and levels of pancreatic enzymes in portal venous effluent were lower in old rats than in younger rats.

BACKGROUND

The effects of ligation of the pancreatic duct and aging on acute pancreatitis caused by taurocholate are still unclear.

METHODS

Young adult and old male Wistar rats were used. Six hours after ligation of the common bile duct in both the duodenum and liver hilus, rats were killed and the pancreata were perfused. Taurocholate or normal saline was injected retrogradely into the common bile duct. The levels of amylase and lipase in the portal venous effluent were determined as markers of damage to the pancreas. The pancreas was also histologically examined after the perfusion experiments using an Image Analysis System.

RESULTS

(1) A nonsignificant elevation of pancreatic enzymes was found in portal venous effluent by the retrograde injection of saline into the common bile duct. Injection of taurocholate caused a marked elevation of enzymes in the effluent for the first 30 min after injection, which then gradually decreased. (2) Basal levels of pancreatic enzymes were significantly higher in the ligation group than in the nonligation group. Injection of saline into the common bile duct had no apparent effect on enzymes in the effluent. In contrast, taurocholate injection into the common bile duct produced a marked increase in enzymes in the portal venous effluent. However, no significant difference was found between the ligation group and the nonligation group. (3) Similar findings were obtained when old rats were used. (4) Although basal levels of enzymes were almost the same in nonligated old and young adults rats, taurocholate injection into the pancreatic duct in old rats resulted in a significant depression of enzymes compared to that in young adult rats. In the ligation group, pancreatic enzymes in the portal venous effluent following taurocholate injection tended to be lower in old rats than in young adult rats. The results were histologically supported in that various degrees of fibrosis were found in the pancreata of old rats.

Pancreatic endocrine dysfunction in rats not expressing the cholecystokinin-A receptor

Cholecystokinin (CCK) has been suggested to modulate insulin output. We have shown that Otsuka Long-Evans Tokushima Fatty (OLETF) rats show little or no expression of the CCK-A receptor gene in the pancreas. We examined whether the CCK-A and CCK-B receptor genes are expressed in the islets and the role of CCK-A receptor in insulin secretion. Gene expressions of CCK receptors were determined by the reverse-transcriptase polymerase chain reaction (RT-PCR) followed by Southern blot hybridization and Northern transfer analysis using LETO rats as controls. Pancreatic endocrine function was examined in perfusion (exogenous CCK stimulation) and meal ingestion (endogenous CCK stimulation) studies. CCK-A receptor mRNA was detected in the islets of LETO rats but not OLETF rats. Expression of the CCK-B receptor gene was detected in both strains by RT-PCR. Insulin secretion was impaired in OLETF rats, but the insulin contents of OLETF and LETO rats were not different. No abnormalities were detected histologically in either strain. These results suggest that the occurrence of pancreatic endocrine dysfunction in OLETF rats may be due to a defect in expression of the CCK-A receptor gene, not to insulin deficiency.

Age-related changes in alpha-adrenoceptor-mediated blood pressure in the rat: relationship between the potency for phenylephrine and the maximum number of binding sites

To study the effects of aging on the blood pressure potency of phenylephrine, 6-, 10- and 40-week-old rats were used. In anesthetized rats, the potency (pD2 value) of phenylephrine on the blood pressure tended to increase with age from 6 to 10 weeks, but significantly decreased thereafter with age from 10 to 40 weeks. Similarly, in pithed rats, the potency of phenylephrine significantly increased, but decreased thereafter. In isolated rat thoracic aorta, the pD2 value of phenylephrine from the contractile responses significantly increased with age from 6 to 10 weeks, but decreased thereafter from 10 to 40 weeks. The change in the potency of phenylephrine on the blood pressure was proportional to the pD2 value of phenylephrine estimated in aortic preparations. The specific binding of [3H]prazosin to single smooth muscle cells of thoracic aorta from different aged rats was saturable. The maximum number of binding sites (Bmax) significantly increased with age from 6 to 10 weeks, but decreased thereafter from 10 to 40 weeks. However, the dissociation constant of [3H]prazosin (Kd) did not alter with age. The changes in the potencies (pD2 values) of phenylephrine on the pressure responses and on the contractile responses were proportional to the logarithm of the maximum number of binding sites. The present study suggests that age-related changes in blood pressure are due to changes in the maximum number of binding sites (receptor density) of alpha 1-adrenoceptors.

Somatostatin inhibits pancreatic exocrine secretion centrally via sympathetic nerves in conscious rats

Somatostatin is known to be a potent inhibitor of pancreatic exocrine secretion, but the mechanism of its effect is not fully understood. The mechanism of the inhibition by centrally administered somatostatin was examined in conscious rats. Rats were prepared with cannulae draining bile and pancreatic juice separately, and with a duodenal cannula, an extrajugular vein cannula and a cerebroventricular cannula. Somatostatin was injected into the left lateral ventricle, and the inhibitory mechanism was examined using vagotomized rats and various drugs that affect sympathetic neurons. Intracerebroventricular administration of somatostatin significantly inhibited pancreatic exocrine secretion stimulated by bile-pancreatic juice diversion. The inhibitory effect was not abolished by vagotomy, pretreatment with propranolol, but was abolished by pretreatment with hexamethonium or phentolamine. The plasma level of somatostatin after its intracerebroventricular administration increased 3-fold, but its intravenous infusion at a rate giving a similar plasma somatostatin level to that produced by its intracerebroventricular injection, had no significant effect on pancreatic secretion. These results suggest that somatostatin inhibits pancreatic exocrine secretion centrally via sympathetic efferent nerves and that alpha-adrenergic receptors have an important role in its inhibitory action.