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Biomedical subjects

P R Holt

Publications and source records attributed to P R Holt.

At least 19 recordsLinked to original sources
PubMed1995

Orally administered opioid antagonists reverse both mu and kappa opioid agonist delay of gastrointestinal transit in the guinea pig.

Kappa(kappa) opioid agonists slow gastrointestinal transit in the guinea pig and the mouse but not the rat. Opioid antagonists naloxone and naltrexone are mu (mu) preferring, while the antagonist nalmefene has more kappa binding activity. When administered orally, the specific opioid antagonists naloxone, naltrexone, and nalmefene are able to reverse the gastrointestinal transit delay caused by orally administered mu and kappa opioid agonists (morphine and U-50, 488H) in a dose dependent fashion as measured by the leading edge of charcoal meal in the guinea pig. Oral naltrexone and nalmefene have significantly more central nervous system (CNS) bioavailability than oral naloxone. However, orally administered naloxone was as effective as either naltrexone or nalmefene in reversing mu opioid agonist induced orocecal transit delays (single agonist dose apparent ED50s = 12.3 +/- 4, 7.3 +/- 4, and 13.5 +/- 6 mg/kg respectively). Nalmefene was more active than either naltrexone or naloxone in its ability to reverse the kappa agonist U-50,488H (single agonist dose apparent ED50s = 18.3 +/- 12*, 37.5 +/- 5, and 61.9 +/- 5 mg/kg respectively; * = p < 0.05). These data confirm the enteric action of orally administered opioids and further supports our earlier findings of the presence of kappa opioid activity in the guinea pig enteric nervous system.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1992

Effects of starvation and refeeding on jejunal disaccharidase activity.

In the rat, starvation lowers jejunal sucrase activity and increases or has no effect upon jejunal lactase activity. The mechanism by which starvation influences these intrinsic microvillus proteins remains unclear. Jejunal sucrase and lactase activities were studied during starvation or refeeding after a three-day fast. Using polyclonal monospecific antibodies, sucrase-isomaltase (SI) and lactase-phlorizin hydrolase (LPH) protein contents were measured in parallel to determine changes in enzyme activation. Sucrase activity and SI protein fell after two and three days of fasting and rose during refeeding. In contrast, lactase activity and jejunal LPH content increased after starvation and decreased after refeeding for 48 hr. For both enzymes, changes in catalytic activity and protein content occurred in parallel. [3H]Leucine incorporation studies in vivo showed more labeling of immunoprecipitable LPH than SI during starvation, but refeeding induced relatively more labeling of SI than of LPH. Therefore, starvation and refeeding produce opposing effects upon jejunal lactase and sucrase activities by modulating LPH and SI protein production and not by modifying enzyme activation.

Animals↗
PubMed1991

Cortisone and thyroxine modulate intestinal lactase and sucrase mRNA levels and activities in the suckling rat.

Glucocorticoids and thyroxine modulate postnatal intestinal sucrase and lactase activities. Whether changes in enzyme activity are accompanied by changes in enzyme mRNA levels were determined in day 6 rats given thyroxine, cortisone, or thyroxine plus cortisone and killed 3 days later. Cortisone induced precocious expression of jejunal sucrase activity which was enhanced when cortisone plus thyroxine was administered; sucrase mRNA changed in parallel. Jejunal lactase activity was unaffected by thyroxine and was increased after cortisone, but not after thyroxine plus cortisone. Jejunal lactase mRNA levels increased equally after cortisone or after cortisone plus thyroxine. Thus, cortisone induces coordinated increases in sucrase and lactase activities and in corresponding mRNA levels. Thyroxine only enhances cortisone induced sucrase expression and antagonizes cortisone by depressing lactase activity post-translationally.

Animals↗
PubMed1991

In vivo immediate early gene expression induced in intestinal and colonic mucosa by feeding.

Since the gut responds rapidly to food intake, the levels of expression of several immediate early genes were measured in mucosa from small and large intestine of rats starved for 3 days or refed. Within 1 h of refeeding, jejunal and ileal c-fos, jun B and zif/268 mRNA and colonic zif/268 dramatically increased. The zif/268 gene in jejunum corresponded in size to the full-length cDNA but, in ileum, an RNA band of about 1.2 kb in size increased greatly after feeding. This represents a physiologic in vivo model for the study of gene regulation associated with intestinal epithelial cellular responses to feeding.

Animals↗
PubMed1991

Posttranslational cleavage of rat intestinal lactase occurs at the luminal side of the brush border membrane.

The intestinal sucrase-isomaltase precursor is cleaved at the brush border membrane by luminal proteases. Whether the lactase precursor also is cleaved by luminal proteases is uncertain. Lactase synthesis and processing was studied in 0- and 15-day-old rats after IP administration of [35S]methionine, and changes in precociously cortisone-induced sucrase-isomaltase were used as an internal control. Mucosal lactase and sucrase-isomaltase were separately immunoprecipitated and analyzed by autoradiography after electrophoresis. In both 0- and 15-day-old rats, mucosal lactase appeared as a 200K lactase precursor band at 30 minutes and as 200K and 225K lactase precursor bands at 60 minutes and was cleaved to form a 130K lactase band 120-240 minutes after labeling; sucrase-isomaltase similarly appeared as 210K and 220K bands at 30-60 minutes and was cleaved to form 140K I and 120K S subunits by 240 minutes in day 15 rats. To determine the role of luminal proteases, intestinal segments were isolated in situ and the luminal contents were flushed 30 minutes after labeling. Unflushed segments were used as controls. Only lactase precursor and sucrase-isomaltase precursor were present 240 minutes after labeling in flushed intestinal segments, but lactase precursor and sucrase-isomaltase precursor were cleaved in unflushed segments. Addition of trypsin or elastase into the lumen of flushed segments resulted in partial cleavage of lactase precursor but not of sucrase-isomaltase precursor. Luminal contents collected from the small intestine of day 15 rats 120 and 240 minutes after labeling showed 35S-labeled 130K and 80K polypeptides in lactase immunoprecipitates. It is concluded that intestinal lactase is synthesized as lactase precursor and transported to brush border membrane and cleaved by luminal proteases, and the amino end polypeptide cleaved from lactase precursor is released into the lumen.

Animals↗
PubMed1991

Food restriction retards age-related biochemical changes in rat small intestine.

Previous studies have demonstrated that the specific activities of several proximal small intestinal mucosal enzymes fall in the aging rat. This reduction was due to a delay in the full expression of activity of these enzymes during epithelial cell transit from the crypt onto the intestinal villus. We now show in the ad libitum fed Fischer 344 rat that jejunal sucrase, maltase, and alkaline phosphatase specific activities do not fall gradually throughout the life span, but are reduced during senescence. Caloric restriction to 60% of ad libitum intake (DR) abolishes or delays this fall in enzyme activity. Jejunal mucosal immunoprecipitable sucrase-isomaltase (S-I) content also falls with age, but sucrase specific activity per molecule of S-I is less in the older ad libitum fed (approximately 45) than in the DR rats (approximately 60). Jejunal lactase activity falls gradually throughout the life span of ad libitum and DR rats, but lactase activity consistently was higher in DR animals. These observations indicate that DR alters the age-related changes in the activity of several enzymes in the rapidly replicating gut mucosa.

Aging↗
PubMed1991

Thyroxine and cortisone cooperate to modulate postnatal intestinal enzyme differentiation in the rat.

Interactions of cortisone and thyroxine (T4) in modulating jejunal sucrase and lactase expression were studied in rats during early postnatal life. Cortisone (50 micrograms/g body wt) precociously induced sucrase activity in days 5-16 rats and enhanced activity thereafter until day 22. T4 (1 microgram/g) plus cortisone evoked greater sucrase expression in day 9 or younger rats. T4 did not induce sucrase expression until day 13. Lactase activity was enhanced in rats younger than day 9 by cortisone, and this effect was abolished when T4 was added. In days 19 and 22 rats, cortisone depressed lactase; with T4, lactase activity was further decreased. T4 alone did not suppress lactase activity until day 19. Quantitation of jejunal enzyme content showed that sucrase catalytic activity was higher in day 22 than 19 or younger rats and lower in rats given T4 than cortisone. In contrast, lactase activity remained constant in all animal groups. In vivo [35S]methionine-labeling studies using day 9 rats showed that cortisone induced de novo synthesis of sucrase and increased 35S incorporation into lactase. Cortisone plus T4 increased 35S incorporation into sucrase further and significantly increased 35S incorporation into lactase. We conclude that 1) cortisone and T4 cooperatively stimulate sucrase expression and reduce lactase activity during early postnatal life and 2) reduction in lactase activity accompanied by increase in lactase synthesis suggests that cortisone and T4 regulate lactase activity at posttranslational level.

Aging↗
PubMed1991

Intestinal lactase expression and epithelial cell transit in hormone-treated suckling rats.

Cortisone- and/or thyroxine (T4)-induced changes in jejunal lactase activity and epithelial cell migration were studied to determine the relationship of these two events. In suckling rats given a single dose of cortisone on day 6, jejunal lactase activity increased by 37% and cell turnover rate by 95% 3 days later, whereas T4 alone induced no changes. After cortisone plus T4, jejunal lactase activity decreased by 23% while cell turnover rate increased by 176%. Among all animal groups, the patterns of lactase expression along the crypt-villus (C-V) axis were similar, being low at the C-V junction, increasing to a high plateau at the mid- or third quarter villus level, and decreasing slightly at the villus tip. The calculated epithelial cell age at half maximum lactase expression in cortisone-treated and cortisone plus T4-treated rats was 30 and 53% younger than in control rats. Maximum lactase activity in villus cells was approximately 45% higher in cortisone-treated than in control or cortisone plus T4-treated rats. Parallel measurements of sucrase and lactase activities along C-V axis showed elevated lactase activity at higher villus positions than lead sucrase activity, suggesting that cortisone action occurs in villus cells. Thus jejunal lactase expression may be modulated by 1) adjusting villus cell age required for maximum expression, 2) altering the level of lactase activity in villus cells, and 3) changing the turnover rate of lactase containing epithelial cells.

Aging↗
PubMed1991

General perspectives on the aged gut.

It is pertinent to ask what clinical conditions would geriatricians most want gastroenterologists to solve. I believe that the three most important are transfer dysphagia, constipation and diarrhea, and fecal incontinence. With transfer dysphagia, the older patient with central nervous system disease simply has forgotten how to swallow. Is it possible, with sensory retraining techniques, to make an impact upon this disabling problem? Although the healthy elderly appear to perceive constipation more often than they actually suffer from it, evacuation clearly is disturbed in hospitalized and nursing-home residents. Can we develop better prokinetic agents to alleviate this problem? Incontinence, more than any other gastrointestinal condition, leads to the transfer of patients from a protected home environment to a chronic-nursing facility. Can we study the pathophysiology of incontinence intensively, as Dr. Nicholas Read's group in Sheffield, England, has done, and develop approaches to managing this important problem? The presentations in this issue of Clinics in Geriatric Medicine may not provide all of the solutions for clinical problems in the elderly that we seek, but it should be a step in the right direction by making salient new information readily available.

Aged↗
PubMed1991

Eosinophil-induced chronic active hepatitis in the idiopathic hypereosinophilic syndrome.

A 19-yr-old man had features of chronic hepatitis with piecemeal necrosis as the sole clinical feature of the idiopathic hypereosinophilic syndrome. Liver biopsy specimens demonstrated the presence of activated eosinophils and, by immunohistochemical staining, major basic protein in areas of hepatic cell damage. The case demonstrates the clinical presentation of the idiopathic hypereosinophilic syndrome as chronic hepatitis and the association between eosinophil infiltration and degranulation with the presence of hepatocyte necrosis.

Adult↗
PubMed1990

Food restriction retards age-related histological changes in rat small intestine.

Previous studies have reported that small and large intestinal crypt hyperplasia and hyperproliferation occur in senescent rats about 27 mo of age. We have studied duodenal and ileal architecture in ad libitum chow-fed rats and have demonstrated that the increase in duodenal crypt depth and crypt hyperplasia do not develop throughout the life span, but become apparent at 21 and 27 mo of age. These crypt hyperplastic features occur without a change in duodenal villus cell number. Ileal villus cellularity increased throughout the life span, suggesting exposure to a gradually increasing luminal nutrient load. Diet restriction to 60% of the ad libitum feeding rate prolonged the life span of animals from 27 to greater than 33 mo and prevented both the duodenal hyperplasia and the increase in ileal villus cell numbers to the age of 27 mo. Thirty-three-month diet-restricted rats did show evidence of duodenal crypt hyperplasia. We conclude that proximal intestinal hyperplasia is a phenomenon that develops in advanced age, but that ileal villus cellularity increases throughout the ad libitum-fed rodent life span. Diet restriction dramatically retards these intestinal changes that are seen with ad libitum feeding and provides an experimental model for the study of age-related cellular changes of the rodent gastrointestinal tract.

Aging↗