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Biomedical subjects

H D Johnson

Publications and source records attributed to H D Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Physiologic and immune responses associated with 48-hour fast of pigs.

We sought to determine the effect of 48 hours of fasting on physiologic and immune responses of pigs. Sixteen crossbred barrows, approximately 8 weeks of age, were housed in a controlled environment (21 degrees C, 45% RH) with feed and water ad libitum. After 10 days, eight pigs were fasted for 48 hours with water available ad libitum; the remaining eight received feed and water ad libitum. Blood samples were obtained by venipuncture before fasting, at the end of 48-hour fasting, and 3 and 10 days later. No significant differences in responses to mitogens PHA or Con A were noted in whole blood or isolated lymphocyte cultures. Changes in numbers of leukocytes, neutrophils, and serum cortisol concentrations, but not of lymphocytes, were significant. The results suggested that short-term fasting transiently reduces the number of neutrophils and increases serum cortisol concentrations, with no effect on blastogenic responses of lymphocytes to selected mitogens.

Animals↗
PubMed1991

Determination of heat-exposure effects on the concentration of catecholamines in bovine plasma and milk.

A reversed-phase high-performance liquid chromatographic method with electrochemical detection has been adapted for the determination of picogram concentrations of norepinephrine and epinephrine in bovine plasma and milk. This method has been used to monitor the levels of these catecholamines when lactating cows are exposed to heat stress under controlled conditions. In response to heat stress, epinephrine concentrations in milk and plasma were similar. However, norepinephrine concentrations in milk were one tenth of that in plasma.

Animals↗
PubMed1991

Assessment of thermal status of somatotropin-injected lactating Holstein cows maintained under controlled-laboratory thermoneutral, hot and cold environments.

Two experiments, with a single-reversal design and 12 cows per experiment, were conducted to study the effects of somatotropin on thermal status of lactating cows under laboratory thermoneutral (18 to 22 degrees C, 30-50% relative humidity), hot (24-35 degrees C, 30-50% relative humidity) and cold (-5 (-) +5 degrees C, 50-55% relative humidity) conditions. Throughout the experiment six cows were injected with somatotropin (25 mg/d) and six with sodium bicarbonate. All injections were started the first day of the 30-d natural environmental period (22-35 degrees C and 41-97% relative humidity for summer experiment, and -5 (-) +5 degrees C and 4-25% relative humidity for winter experiment) before the cows were exposed alternatively to laboratory thermoneutral and hot or cold environments. The somatotropin-treated cows had higher energy intake (13 and 17%), heat production (19 and 25%), heat loss (36 and 24%) and milk energy (40 and 49%), than control cows under thermoneutral and hot conditions, respectively. The somatotropin-treated cows had higher heat production (18 and 10%), respiratory heat loss (27 and 17%) and milk energy (14 and 25%) than control cows under thermoneutral and cold conditions, respectively. The increased heat production associated with somatotropin was accompanied by increased heat losses. Part of the increased heat production was attributed to the increased milk energy and energy intake. These results suggest that increased heat production during somatotropin treatment was within the range that could be dissipated by the cows.

Animals↗
PubMed1991

Effects of somatotropin on milk yield and physiological responses during summer farm and hot laboratory conditions.

The effects of bST on performance and physiological responses of lactating cows was studied under farm summer and laboratory heat conditions. Twelve cows, 90 to 50 d postpartum, were injected with either bST or vehicle solution for 30 d under farm summer and 10 d under either laboratory thermoneutral or heat conditions. Somatotropin increased milk yield by 6.1 (21%), 8.1 (32%), and 7.3 kg (35%) under the farm summer, laboratory thermoneutral, and heat conditions, respectively. Somatotropin also increased milk fat by 15 and 19% and dry matter intake by 16 and 18% under laboratory thermoneutral and heat conditions, respectively. Somatotropin increased the efficiency of feed conversion into milk without any significant changes in body weight and temperatures. Somatotropin reduced plasma concentrations of triiodothyronine and cortisol and had no effect on plasma prolactin and insulin concentrations. Somatotropin did not increase water intake; however, hematocrit was decreased. The results suggest that stimulatory effects of bST on milk production are still observed on heat-stressed cows without any significant indications of additional heat stress.

Animals↗
PubMed1990

Effect of farm and simulated laboratory cold environmental conditions on the performance and physiological responses of lactating dairy cows supplemented with bovine somatotropin (BST).

A study was conducted to evaluate the effect of bovine somatotropin (BST) supplementation in twelve lactating dairy cows maintained in cold environmental conditions. Six cows were injected daily with 25 mg of BST; the other six were injected with a control vehicle. Cows were maintained under standard dairy management during mid-winter for 30 days. Milk production was recorded twice daily, and blood samples were taken weekly. Animals were then transferred to environmentally controlled chambers and exposed to cycling thermoneutral (15 degrees to 20 degrees C) and cycling cold (-5 degrees to +5 degrees C) temperatures for 10 days in a split-reversal design. Milk production, feed and water intake, body weights and rectal temperatures were monitored. Blood samples were taken on days 1, 3, 5, 8 and 10 of each period and analyzed for plasma triiodothyronine (T3), thyroxine (T4), cortisol, insulin and prolactin. Under farm conditions, BST-treated cows produced 11% more milk than control-treated cows and in environmentally controlled chambers produced 17.4% more milk. No differences due to BST in feed or water intake, body weights or rectal temperatures were found under laboratory conditions. Plasma T3 and insulin increased due to BST treatment while no effect was found on cortisol, prolactin or T4. The results showed that the benefits of BST supplementation in lactating dairy cows were achieved under cold environmental conditions.

Animals↗
PubMed1990

Suppressed peripheral blood lymphocyte blastogenesis in pre- and postpartal sheep by chronic heat-stress, and suppressive property of heat-stressed sheep serum on lymphocytes.

Phytohemagglutinin (PHA) and concanavalin A (Con A)-induced blastogenesis of peripheral blood lymphocytes was examined in heat-stressed pre- and postpartal sheep. The peak responses of lymphocytes to PHA and Con A in heat-stressed sheep revealed significant reduction before and after parturition compared with those in the corresponding control animals kept under thermoneutral conditions. Furthermore, the effect of serum from control or heat-stressed sheep on PHA-induced lymphocyte blastogenesis was examined. Supplementation of serum from heat-stressed sheep significantly suppressed the blastogenesis of lymphocytes obtained from healthy sheep, bovine, and human donors. Unlike dexamethasone, heat-stressed sheep serum did not inhibit IL-2 production by PHA-stimulated human peripheral blood lymphocytes. These results indicate that the immunosuppression of heat-stressed sheep is in part mediated by serum factor(s) that can modulate T-cell function in a species nonspecific manner.

Animals↗
PubMed1989

Suppression of T-lymphocyte blastogenesis by ovine trophoblast protein-1 and human interferon-alpha may be independent of interleukin-2 production.

Cells derived from the trophoblast tissue of a day 15 sheep conceptus released substances that inhibit incorporation of [3H]thymidine into phytohemagglutinin (PHA)-stimulated ovine lymphocytes. This effect was partially reversed by addition of antiserum to ovine trophoblast protein-1 (oTP-1), a major secretory product of day 13-21 sheep conceptuses and a protein structurally and functionally related to alpha-interferons (IFN-alpha). Human IFN-alpha, unlike dexamethasone, inhibits phytohemagglutinin-induced lymphocyte blastogenesis without reducing interleukin-2 (IL-2) production by the cultures, and conditioned medium containing IL-2 does not promote [3H]thymidine incorporation into ovine lymphocytes when oTP-1 is present. Thus, oTP-1, by virtue of being an IFN, may have a local immunomodulatory role by selectively inhibiting the proliferative responses of certain maternal immune cells to IL-2.

Animals↗
PubMed1989

Some hormonal characteristics of high and low yielding Holstein cows and water buffaloes located in temperate and subtropical environments.

The present study was carried out on 18 Holstein cows located in Missouri, USA (Holstein-M), 32 Holstein cows located in Egypt (Holstein-E), and 32 Egyptian water buffaloes (Buffaloes-E). Half of each group was high yielders and the other half was low with a mean daily milk yield of 32.2 and 18.6 kg for Holstein-M, 14.6 and 6.7 kg for Holstein-E, and 7.2 and 1.8 kg for Buffaloes-E, respectively. Blood samples were collected after the morning milking. Mean plasma thyroxine and triiodothyronine concentrations were significantly higher in Holstein-M than those in Holstein-E or Buffaloes-E. In all animal groups, the high yielders generally had lower plasma thyroxine and antidiuretic hormone but higher plasma triiodothyronine contents than the low yielders. Buffaloes had lower plasma cortisol and 9-fold higher plasma antidiuretic hormone as compared with the two Holstein groups.

Analysis of Variance↗
PubMed1989

Effect of xylazine in heifers under thermoneutral or heat stress conditions.

A study was performed to assess the effect of xylazine HCl (0.1 mg/kg of body weight, IV) in heifers maintained at thermoneutrality (18 C, 42% humidity) or under heat stress (33 C, 63% humidity) conditions. Xylazine caused 50 and 70% decreases in serum insulin concentrations in the thermoneutral and heat-stressed heifers, respectively. Xylazine-induced hypoinsulinemia was associated with hyperglycemia. In the thermoneutral group, serum glucose concentrations increased from a basal concentration of 75 mg/dl to 150 mg/dl after 15 minutes. In the heat stress group, the serum glucose concentration increased from 65 mg/dl to 105 mg/dl. Hyperglycemia peaked at 2 hours and remained high for 6 hours after xylazine administration. Heat-stressed heifers took a longer time (107 minutes) to stand than did heifers under thermoneutral conditions (41 minutes). The time to regain sensation to pain was significantly prolonged in heat-stressed heifers. Xylazine had no effect on body temperature and respiration rate in heifers under the thermoneutral condition, whereas it markedly induced hyperthermia and suppressed respiration rate in the heat-stressed heifers. Furthermore, the pulse rate was slightly decreased in thermoneutral heifers and was markedly decreased in the heat-stressed heifers.

Animals↗
PubMed1987

Physiological, productive, and economic benefits of shade, spray, and fan system versus shade for Holstein cows during summer heat.

During the 1984 summer, effects of spray and fan in freestall areas and feeding areas on milk yield, plasma growth hormone and prolactin, freestall utilization, and economic significance for Holstein cows were studied. Weekly milk and rectal temperatures at morning and afternoon milkings were higher for cows in shade than in shade with spray and fan cooling. Compared with rectal temperature, milk temperature measured in the clawpiece provided a more reliable indicator of heat stress than in the milk meter. Diurnal pattern of rectal temperature from 4-h measurements showed an average of 12 h in which maximal rectal temperatures of cows in shade were greater than 39 degrees C, but cows in the shade plus spray plus fan group had rectal temperatures below 39 degrees C all day. Plasma growth hormone was higher and prolactin lower for cows in shade plus spray and fan than cows in shade only. Cows cooled with spray and fan under shade produced 2 kg/cow per d more than cows in shade alone. Economic analysis showed a net income of 22 cents/cow per day for spray plus fan under shade. Results suggest that milk temperature is a practical technique to assess heat stress in dairy cattle, and the use of spray plus fan is a profitable means to maximize cow comfort and lessen stress-induced decline in milk production.

Animals↗
PubMed1985

Prolactin and its involvement in fluid regulation in the bovine.

Plasma prolactin (PRL) concentrations, osmolality, water consumption, feed intake, urine excretion, and fecal water output were determined in twelve steers of 3 breeds exposed to 5 feed and water regimes. Breed differences were found in water intake and plasma PRL concentrations when feed and water were ad lib., however, during any of the other 4 treatments, responses were similar between breeds. During dehydration and feed restriction, water intake, urine, fecal water, and plasma prolactin decreased; however, during hydration and refeeding such changes were not as clearly related. No consistent relationships between plasma prolactin and osmolality were found. Data suggests that PRL's role in fluid regulation in the bovine is most likely associated with alterations in renal hemodynamics rather than by changes in plasma osmolality.

Animals↗
PubMed1985

Plasma antidiuretic hormone (ADH) concentrations in cattle, during various water and feed regimes.

Twelve steers of three different breeds were exposed to five feed and water regimes in order to characterize changes in plasma antidiuretic hormone (ADH) concentrations. No breed differences were found in plasma ADH concentration. Plasma ADH concentration rose (4.2 to 22.0 pg/ml) during dehydration. By 3 hr hydration, plasma ADH concentrations dropped dramatically (over 50%) to 9.2 pg/ml. No changes in plasma ADH concentrations occurred during feed restriction and refeeding. Hematocrit percentages were also determined and differences are hypothesized to relate to probable differences in environmental adaptability and genetic selection for meat or milk production among the three breeds.

Animals↗
PubMed1985

Spray cooling effects on milk production, milk, and rectal temperatures of cows during a moderate temperate summer season.

During summer 1982, responses of lactating Holstein and Guernsey cows were measured by milk temperature recorded by a Digital Dataloger with thermocouples attached to Boumatic flow meters. Maximum air temperature and temperature-humidity index averaged 30.8 degrees C and 75.6 for July. Breed did not affect milk temperature, but within-breed milk temperature increased with production. In a second study, benefits of spray cooling were evaluated with 24 Holsteins in midlactation assigned randomly to two groups of 12 and maintained under loose-housing conditions. Spray nozzles were installed in the walkways and under the manger shade for the spray treatment group. Maximum temperature and temperature-humidity index during the spray study were 27 degrees C and 73.9. Rectal temperature taken following milking averaged less for treatment than control (38.8 versus 39.1 degrees C). Milk temperature was similar (37.8 versus 38.1 degrees C). Daily milk yield was .70 kg higher than controls. Milk temperature may provide reliable indication of climate stress similar to rectal temperature, and spray cooling improves cow comfort and lessens summer decline of milk production.

Animals↗
PubMed1985

Effect of growth hormone on milk yields and related physiological functions of Holstein cows exposed to heat stress.

Responses of milk production and other physiological functions to daily subcutaneous injections of bovine growth hormone (16.6 mg/cow) were studied in six Holstein cows in midlactation under environmental heat stress. Five days were assigned for each treatment of thermoneutral (18.3 degrees C), heat (28.9 degrees C), heat plus growth hormone, and heat. Each period was preceded by at least 3 days of adjustment. Feed and water were available ad libitum. Feed intake, milk production, and rectal temperature were measured twice daily. Blood, energy metabolism, and body weight were measured every 1st, 3rd, and 5th day of each period. Administration of growth hormone under heat stress increased milk production by 3.8 and 12% and fat yield by 9.5 and 12.7% over heat and heat. Feed intake declined by 5.8% with no significant increase of heat production or body weight loss during treatment with bovine growth hormone. Heat increased somatic cell concentration.

Animals↗
PubMed1979

High-performance liquid chromatographic analysis of biogenic amines in biological materials as o-phthalaldehyde derivatives.

A remarkably sensitive, simple and selective reversed-phase high-performance liquid chromatographic (HPLC) method has been developed, allowing, for the first time, the direct measurement of histamine, norepinephrine, octopamine, normetanephrine, dopamine, serotonin and tyramine in a single sample of plasma (2 ml), tissue (0.2 g), or urine. The biogenic amines were modified by pre-column derivatization with o-phthalaldehyde which stabilizes the molecules, aids in extraction, and improves HPLC detection at the nanogram level. To minimize losses during the sampling procedure a careful collection procedure was designed. We developed a simple sample cleanup in which the samples were thawed, neutralized with KOH, immediately derivatized, extracted into ethyl acetate (EtOAc) and then chromatographed by HPLC. The derivatives were stable in EtOAc for more then 24 h. Interfering amino acids were removed from the EtOAc by partitioning twice with Na2HPO4 buffer (pH 10.0). Complete separation was achieved in ca. 60--90 min on a muBondapak phenyl column using a stepwise gradient of acetonitrile and/or methanol-phosphate buffer (pH 5.1). A variable wavelength fluorometer with a 5-microliter flow-cell was used (excitation 340 nm; emission 480 nm). Linearity ranged from 200 pg to 50 ng onto the column. Precision (R.S.D.) for retention times was 1% and for derivatization and injection 2.5%. Recoveries of the seven biogenic amines from plasma spiked with 25 ng/ml averaged 70%, with a relative standard deviation of 6%. Separation studies were also done using a muBondapak C18 column. The effects of various eluents are presented. Gas-liquid chromatography was also investigated but lacked the sensitivity achieved by HPLC. The HPLC method is used routinely for the determination of biogenic amines in plasma from pigs with malignant hyperthemia and thermally stressed bovine. Significant differences in levels of biogenic amines were noted between stressed and non-stressed animals. Data on rat brain tissue samples were compared with the trihydroxyindole method and canine heart tissue was analyzed for ventricular norepinephrine and dopamine. Application of the method to urine from normal persons and a patient with a brain tumor has been demonstrated.

Animals↗
PubMed1978

Effect of adrenocorticotropic hormone on plasma glucocorticoids and antidiuretic hormone of cattle exposed to 20 and 33 C.

Four open, dry Holstein cows in the University of Missouri Climatic Laboratory were used to study the effect of adrenocorticotropic hormone administration on glucocorticoids and antidiuretic hormone of plasma in two reversal trials at thermoneutral (20 C, 50% relative humidity) and heat (33 C, 50% relative humidity) conditions. Average glucocorticoids (saline versus adrenocorticotropic hormone) at thermoneutral were 8.3 and 41.2 ng/ml while values for heat were 6.2 and 40.4 ng/ml. The effect of heat on glucocorticoids of plasma was not significant. Injection of adrenocorticotropic hormone under thermoneutrality and heat caused a marked increase in antidiuretic hormone within 5 min which lasted to 120 min. At thermoneutral average antidiuretic hormone levels (saline versus adrenocorticotropic hormone) were .5 and 1.9 pg/ml while values for heat were 1.8 and 3.6 pg/ml. Antidiuretic hormone concentrations under heat were higher than thermoneutral in cows injected with saline and andrenocorticotropic hormone. The fast response of antidiuretic hormone of plasma to exogenous adrenocorticotropic hormone suggests that adrenocorticotropic hormone might act directly at higher levels of the central nervous system causing release of antidiuretic hormone.

Adrenocorticotropic Hormone↗