Biomedical subjects

G D Potter

Publications and source records attributed to G D Potter.

At least 19 recordsLinked to original sources

PubMed1991

Bile acid stimulation of cyclic AMP and ion transport in developing rabbit colon.

Bile acids elicit Cl secretion and increases in short circuit current (Isc) in rabbit distal colon in vitro in adult but not newborn animals. In this investigation we found that concentrations of taurodeoxycholic acid (TDC) as low as 50 microM significantly increase cyclic AMP (cAMP) in adult but not newborn colon. Further, blocking the increases of cAMP in adult colon with 3,4,5-trimethoxybenzoate 8-(N,N-dimethylamino) octyl ester (TMB-8), partially inhibited the effect of TDC on Cl secretion. TMB-8 did not block the effect of increases in cAMP seen with vasoactive intestinal peptide (VIP), theophylline, or forskolin. When newborn colon was exposed to 1 mM TDC, limited Cl secretion was elicited. Increased cAMP is not seen in newborn colon where TDC-induced secretion is absent. Thus, increases in cAMP may represent one part of the coupling of TDC stimulation to Cl secretion.

Animals↗

PubMed1990

Intestinal development and regeneration.

This first article of a new series on "cellular" gastroenterology focuses on the embryogenesis and neonatal development of the gut. In this context, the effects of malnutrition, morbidity, and trauma on intestinal histodynamics are discussed, as are compensatory adaptations analogous to those in the circulatory responses to heart failure.

Adult↗

PubMed1990

Atrial natriuretic factor and cyclic guanosine monophosphate: ion transport in rat colon in vitro and in vivo.

The role of atrial natriuretic factor receptors in the colon is uncertain. Accordingly, the effects of atrial natriuretic factor in vivo and in vitro were studied. In vivo perfusion of the colon in Sprague-Dawley rats was used to measure Na+, K+, Cl-, and water transport, while atrial natriuretic factor was infused into the jugular vein at 0.5 or 1.0 micrograms.kg-1.min-1. In vitro experiments in Ussing chambers measured short-circuit current and ion fluxes before and after atrial natriuretic factor administration. Because cyclic guanosine monophosphate is thought to be a second messenger for atrial natriuretic factor, short-circuit current was also determined before and after exposure to 8-Br-cyclic guanosine monophosphate. Plasma atrial natriuretic factor (atriopeptin III) levels were determined by radioimmunoassay. The in vivo transport of water, sodium, and chloride and the secretion of potassium were not altered by atrial natriuretic factor infusion. In vitro studies showed no change in Na+ or Cl- transport or change in short-circuit current. Plasma atrial natriuretic factor concentrations increased from 139 +/- 55 pg/mL to 1385 +/- 396 pg/mL during infusion, and urine output increased from 12.6 +/- 0.5 microL/min to 37.4 +/- 2.9 microL/min (P less than 0.05). In contrast, 8-Br-cyclic guanosine monophosphate in vitro caused a significant (P = 0.0004) increase in short-circuit current from 1.2 +/- 0.2 to 2.9 +/- 0.3 microEq.cm-2.h-1.

Animals↗

PubMed1989

Phenamil inhibits electrogenic sodium absorption in rabbit ileum.

Electrogenic Na absorption, independent of either nutrients or other ions, occurs in the rabbit ileum. However, unlike electrogenic Na absorption in the distal colon and other tight epithelia, this ileal transport system is not inhibited by amiloride. Because of this amiloride insensitivity, ileal electrogenic Na absorption has been poorly characterized. To more clearly delineate the underlying mechanisms of this pathway, we examined the effects of phenamil, an amiloride analogue, on ion fluxes and electrical parameters in rabbit ileum in vitro under short-circuit conditions. Phenamil has been shown to have a high affinity for Na channels, but minimal effect on Na-H exchange. Amiloride (10(-8) through 10(-4) M) had a minimal effect on short-circuit current. In contrast, phenamil induced a significant decrease in short-circuit current; the maximal effect was seen at 10(-4) M phenamil. There was an associated decrease in conductance at 10(-4) M phenamil. Ion flux studies were performed in normal, chloride-free and bicarbonate-free Ringer's solution; under each condition, 10(-4) M phenamil inhibited mucosal-to-serosal Na flux, net Na flux, and short-circuit current without significantly altering other fluxes. Phenamil did not inhibit the electrical response to either 10 mM glucose or 1 mM theophylline, indicating that the drug did not block either nutrient-coupled electrogenic Na absorption or electrogenic Cl secretion, and did not inhibit sodium-potassium-stimulated adenosine triphosphatase. These results demonstrate that electrogenic Na absorption in rabbit ileum may be blocked by the amiloride analogue phenamil, suggesting that, in this epithelium, Na absorption may occur via Na channels in which the amiloride-binding site has been significantly altered.

Amiloride↗

PubMed1989

Electrogenic sodium transport in the developing rabbit cecum.

The adult rabbit cecum absorbs Na by an electrogenic, Cl-independent process that is inhibited by the amiloride analogue phenamil. In the colon, this transport system is unique to the cecum. Because the developing colon exhibits many specialized functions, we have now examined the development of electrogenic Na transport in the newborn rabbit. Cecal tissue from animals between 7 and 38 days old was mounted in modified Ussing chambers for measurement of Na and Cl flux (J) and the short-circuit current (Isc). At 7-10 days, the (Isc) was only 0.8 +/- 0.18 microEq cm-2 h-1, but by 35-38 days it had increased to 4.6 +/- 0.79 microEq cm-2 h-1. The Na transport increased in parallel with Isc; JNanet = -0.49 +/- 0.33 microEq cm-2 h-1 at 7-10 and 4.7 +/- 1.6 microEq cm-2 h-1 at 35-38 days. The Na transport was not inhibited by phenamil (10-4 M) at 7-10 days, but by the 35-38-day period, phenamil reduced the JNanet to 1.6 +/- 0.37 microEq cm-2 h-1. The Cl secretion was not stimulated by theophylline in the 14-16-day-old cecum, nor was Na absorption stimulated by epinephrine. The rabbit cecum does not demonstrate electrogenic Na absorption until after the 4th week of life.

Animals↗

PubMed1989

Potassium secretion in response to taurodeoxycholic acid in the newborn rabbit colon.

The newborn colon fails to secrete Cl in response to concentrations of dihydroxy bile acid that cause Cl secretion in adult colonic tissue in vitro. Bile acids also cause secretion of potassium in adult tissues, but there is no information concerning bile acid effects on potassium transport in newborn colon. We mounted newborn rabbit distal colon in Ussing chambers specially designed for newborn colon and measured potassium transport. Basal potassium transport was secretory. Taurodeoxycholic acid, 100 microM, (TDC) decreased JKnet from -0.76 +/- 0.07 to -0.94 +/- 0.11 microEq cm-2 h-1, p less than 0.05, without increasing Isc. Serosal ouabain, 0.1 mM, abolished the secretory response to TDC. Mucosal Ba2+, a potassium channel blocker in many epithelia, did not inhibit K secretion. Similar serosal exposure to TDC in adult colon tissues decreased JKnet from -0.09 +/- 0.29 to -1.63 microEq cm-2 h-1, p less than 0.01, and increased Isc. We conclude that, although the chloride secretory response to dihydroxy bile acids is absent in the newborn, K secretion is elicited in the newborn, similar to the adult colon.

Animals↗

PubMed1989

Isolated sphenoid sinus disease.

Forty-three cases of isolated sphenoid sinus disease were reviewed. In 33 cases, headache was a presenting symptom. Seven of 29 cases of inflammatory disease and nine of 13 patients with tumors of the sinus presented with cranial nerve findings. When nonspecific visual disturbances were eliminated, two of 29 cases of inflammation and eight of 13 cases of tumors of the sphenoid sinus had cranial nerve deficits. Ten of 12 CT scans performed on patients with tumors of the sinus demonstrated bony erosion or perisinus extensions. This was not found in any of the 27 scans of patients with inflammatory disease. A thorough cranial nerve examination and a CT scan should be performed early in patients who present with vague and unusual headaches.

Adolescent↗

PubMed1989

Growth performance of yearling horses grazing bermudagrass pastures at different grazing pressures.

Body weight gains and height at the withers were measured in yearling geldings grazing bermudagrass (Cynodon dactylon [L.] Pers.) pastures with neither energy nor protein feed supplementation at stocking rates of 6.7, 8.0, 9.5 and 12.4 yearlings per hectare. Weekly forage samples were taken to estimate the quantity and quality of available forage. These samples were clipped and separated into three equal lengths to characterize upper, middle and lower thirds of the canopy and to determine relationships between available forage and yearling growth rate. Average daily gain was influenced by stocking rate, but gain in height was not affected by stocking rate. Average daily gain ranged from -.31 to .37 kg/d and was negatively related to stocking rate. A quadratic relationship between available forage and ADG was detected. However, a linear relationship between ADG and available forage in top layers of the canopy indicated that animal performance might have been limited by availability of top layer forage in pastures subjected to light grazing pressure.

Analysis of Variance↗

PubMed1988

Digestion of hay protein in different segments of the equine digestive tract.

Mature ponies fitted with permanent ileal cannulas were used in a 3 X 3 Latin square experiment to quantify prececal, postileal and total tract digestion of hay protein. Coastal Bermuda grass (CB), containing 11.7% crude protein, and two qualities of alfalfa, containing 15.0% (low-protein alfalfa; LA) and 18.1% (high-protein alfalfa; HA) crude protein, were fed in coarsely chopped form at 2% of body weight daily. Total tract apparent digestibility of the N in HA (73.8%) was higher than that in CB (57.0%; P less than .05) and was slightly higher than that in LA (66.1%; P less than .10). Nitrogen in LA was apparently more digestible than that in CB (P less than .05). Apparent prececal digestibilities of N in LA and CB were 1.3% and 9.6%, respectively, and were lower (P less than .05), or tended to be lower (P less than .10), than the 21.0% observed for HA. In relative terms, an average of 9.4% of the total N digestion occurred in the upper tract when CB and LA were fed, whereas 28.5% of total N digestion occurred in the foregut when HA was fed. There was a slightly higher concentration of total plasma free amino acids (P less than .10) at 1 h postfeeding when horses were fed alfalfa. Also, N retention was higher when ponies were fed HA (P less than .05) than when LA or CB were fed. Apparent postileal N digestibility was 52.5% for CB, 65.7% for LA and 66.9% for HA. Differences were not significant, and the large intestine appeared to compensate for the inefficiency of N digestion in the upper tract.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗

PubMed1988

Nitrogen metabolism in mature horses at varying levels of work.

Nitrogen metabolism was measured in five mature geldings performing varying levels of work that simulated race training. Following an initial maintenance period without forced exercise, workload was increased in succeeding 18-d periods by doubling the distance the horses were galloped in each period from period 2 through 4. A 4-d N balance experiment was conducted at the end of each 18-d period. The maximum distance galloped daily, which was in period 4, was repeated in period 5. Then, workloads were decreased through period 7. Nitrogen balance was determined in two additional periods, 8 and 9, while the geldings were at maintenance with no forced exercise. Geldings were fed diets containing similar protein-to-calorie ratios in all periods. Nitrogen retention increased (P less than .05) as workload increased from period 1 to period 3 and remained elevated throughout the rest of the experiment. Nitrogen retention did not (P greater than .05) decrease from highest values, observed at maximum workload during periods 4 and 5, until period 9, which was 34 d postexercise during a maintenance period. Nitrogen retention was higher (P less than .05) following training than before training.

Animals↗

PubMed1988

Lower gastrointestinal bleeding.

Lower gastrointestinal bleeding remains an important medical emergency. Most lower gastrointestinal bleeding is now known to come from angiodysplasia or diverticular disease. Accurate angiographic and colonoscopic diagnosis may lead to a better focus for treatment and improved survival.

Arteriovenous Malformations↗

PubMed1987

Taurodeoxycholate and the developing rabbit distal colon: absence of secretory effect.

Failure to absorb bile acids by the ileum leads to fluid secretion by the colon and diarrhea in adults. The infant ileum, however, does not actively transport bile acids. Therefore, we investigated the effect of taurodeoxycholic acid (TDCA) on ion transport in the colon of rabbits 7-10 days old. We mounted distal colon from infant and adult rabbits in modified Ussing chambers and exposed the mucosal or serosal surfaces to TDCA. In the adult, 50 microM TDCA produced an increase in short-circuit current (delta Isc = 1.0 +/- 0.3 mu eq . h-1 . cm-2, P less than 0.05) and Cl secretion. In the infant, the effect was different, Isc was reduced (delta Isc = -1.1 +/- 0.2 mu eq . h-1 . cm-2, P less than 0.01) and ion flux was not altered. Microscopy demonstrated that the infant epithelium was not significantly damaged by exposure to TDCA at these concentrations. The infant colon was, however, capable of a secretory response to a variety of agonists including theophylline, carbachol, bradykinin, serotonin, and 12,13-dibutyryl phorbol ester. The infant rabbit distal colon lacks a secretory response to TDCA during that period when the ileum cannot transport bile acids.

Animals↗

PubMed1987

Use of different nonglycolysable sugars to maintain stallion sperm viability when frozen or stored at 37 degrees C and 5 degrees C in a bovine serum albumin medium.

Bovine serum albumin (BSA) diluents containing lactose, raffinose or sucrose were not different (P greater than 0.05) in their ability to maintain stallion sperm viability, as determined by percentage motile spermatozoa (PMS) and their rate of forward movement (RFM), when stored at 37 or 5 degrees C for 24 h. These diluents did promote a higher (P greater than 0.05) PMS and RFM, when compared with BSA diluents containing arabinose or galactose. The BSA-arabinose and BSA-galactose diluents did not differ (P less than 0.05) in their ability to support sperm viability and were detrimental to spermatozoa. The fertility of freshly collected and diluted spermatozoa was not different (P greater than 0.05) when extended in BSA diluents containing lactose, raffinose or sucrose. There was no difference (P greater than 0.05) in PMS and RFM of frozen-thawed stallion spermatozoa when the spermatozoa were frozen, thawed and incubated at 37 degrees C for 180 min in BSA diluents containing lactose, raffinose or sucrose. Spermatozoa from 6 of 8 stallions did not survive the freezing process. A one-cycle conception rate of 32% was obtained from frozen-thawed spermatozoa extended in BSA diluents containing lactose, raffinose or sucrose. This rate was 78% of the conception rate obtained when the same mares were inseminated with fresh semen in a subsequent study (41%).

Animals↗

PubMed1987

Fine structure of the follicular oocyte of the horse.

Oocytes recovered by follicular aspiration were evaluated by light and transmission electron microscopy. Of the 22 oocytes, 4 exhibited characteristics of degeneration, and the remaining 18 were in various stages of meiotic development. Of the non-degenerate oocytes, 14 were in the germinal vesicle stage, 2 had undergone nuclear membrane disintegration, 1 displayed chromosomes in late metaphase I-early anaphase I, and 1 oocyte was in the process of extrusion of the first polar body. Although some oocytes retained complete cumulus cell investments, oocytes were predominantly enclosed only by the corona radiata. Ultrastructural evaluation revealed that follicular oocytes of the horse are similar to those of other mammals. An abundance of vesicular agranular endoplasmic reticulum in horse oocytes was the most obvious difference. Variation in intracellular organization seemed to be primarily dependent upon stage of meiotic development.

Animals↗

PubMed1987

Ultrastructure of cryopreserved horse embryos.

Embryos were recovered non-surgically at about Day 6 after ovulation from 15 Quarter horse-type mares and were evaluated for morphological changes which may occur because of exposure to the cryoprotectant and/or cryopreservation. Electron microscopy was used to elucidate the fine structure of intracellular organelles which, if damaged, could cause cellular death. The horse embryo does not totally re-expand in the 10% glycerol freezing medium, nor will it completely re-expand in the isotonic holding medium following glycerol removal whether or not the embryo has been frozen. Embryos in this study were frozen by the same protocol which had resulted in a 30% pregnancy rate for similarly frozen embryos. Junctional complexes between trophoblast cells, as well as the plasma and nuclear membranes of trophoblast and inner cell mass (ICM) cells, were intact after treatment in all embryos. Changes in lipid droplets and some mitochondrial degeneration were observed in the ICM cells of the glycerol-treated embryos. The change in the lipid was not observed in the frozen-thawed embryos, but mitochondrial changes were evident in the trophoblast and ICM cells, with the most extensive mitochondrial damage in the ICM cells.

Animals↗

PubMed1987

Exogenous hormone regimens to utilize successfully mares in dioestrus (days 2-14 after ovulation) as embryo transfer recipients.

Two hormone regimens were utilized for recipient mares which were 2-14 days after ovulation at the time of non-surgical embryo transfer. In Exp. I, 20 embryos were transferred non-surgically into recipient mares which had been given 22 mg altrenogest daily starting the day of recipient ovulation. Higher (P less than 0.05) pregnancy rates (50% vs 0%) were obtained in mares which were 2-6 days after ovulation at the time of transfer compared with mares which were 7-12 days after ovulation. In Exp. II, on the day the donor mare ovulated (Day 0), 10 mg PGF-2 alpha were given to the recipient mare at 0 h, 20 mg oestradiol cypionate at 12, 24 and 36 h, 500 mg progesterone in oil at 48 h and then 22 mg altrenogest at 60, 72 and 96 h. Altrenogest (22 mg/day) was continued until Day 28 (fetal heart beat). The pregnancy rate (58% vs 10%) was higher (P less than 0.05) for the 12 recipient mares which were 10-14 days after ovulation than for the 10 mares that were 5-8 days after ovulation when treatment began. Early embryonic loss was detected in 4/8 pregnant recipient mares between Days 21 and 28 of gestation. We suggest that mares which are 2-14 days after ovulation and not in ovulation synchrony with the donor may be used as embryo transfer recipients; mares which are in early dioestrus can be given altrenogest while those in mid- to late dioestrus can be placed on the more complex hormone regimen.

Animals↗

PubMed1986

Historical perspectives on selected health and safety aspects of nuclear weapons testing.

This paper presents a general review of public safety standards as adapted by the nuclear weapons testing program in the United States, and the impact of these changing standards on the nuclear testing program itself. The review notes the importance of improvements in diagnostic instrumentation and methodologies from a relatively simple degree of sophistication to their current high level. Use of the improved methodologies uncovered a serious oversight affecting human exposure, namely, that of not recognizing the relative importance of all potential transport/dosimetric pathways for risk assessment. The testing program, from its inception in the Pacific in 1946 to the present time in Nevada, is viewed from the perspective of providing improved radiation protection to the general public.

Health Physics↗

PubMed1986

Glucose-coupled sodium absorption in the developing rat colon.

The developing mammalian colon is lined by villi and is capable of glucose and amino acid absorption at birth in the rat. Neither the point at which this capacity is lost nor the effect of the capacity for glucose transport on Na absorption has been studied. We have now applied a system for perfusion of the lumen of in vitro segments of colon from 20-day-old fetal rats, and pups between 6 and 8 days old, to measure Na transport and transepithelial potential difference (PD). The lumens of colons from animals at both ages were perfused with solutions containing glucose or mannitol and 22Na. Net Na transport was 164 +/- 37 mu eq X h-1 X g dry weight tissue perfused-1, as determined by the difference between lumen-to-bath and bath-to-lumen flux in fetal rat colons at day 20. Glucose increased the lumen-to-bath flux by 90 +/- 35 mu eq X h-1 X g-1. PD was immediately increased from -1.7 +/- 0.16 to -8.0 +/- 0.96 mV (lumen with respect to bath) by the addition of glucose, and the change in PD was inhibited by 10(-4) M phlorizin. The PD response to glucose was lost at day 2 of life, but the villus epithelium persisted. Amiloride, 10(-4) M, did not alter PD or Na transport at either age. We conclude that the fetal rat colon exhibits glucose-dependent Na flux at birth but that this property is lost by 6-8 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗