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Biomedical subjects

A L Johnson

Publications and source records attributed to A L Johnson.

At least 217 records · Page 12Linked to original sources

Effects of physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare.

Four studies were conducted to evaluate the effects of several physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare. An increase in prolactin measured in response to administration of thyrotropin-releasing hormone (TRH; 50 micrograms, iv) was found not to vary (P = .20) in mares in estrus compared with mares in diestrus (5 to 10 d post-ovulation). Administration in the dopamine receptor blocker, metoclopramide (25 or 100 mg, im), rapidly increased serum prolactin, and the response was dependent on dose administered (total prolactin measured for 420 min was 3,362.7 +/- 182.1 ng for 25 mg, and 4,485.7 +/- 212.6 ng for 100 mg administered im; P less than .05), but not on route of injection (3,026.3 +/- 492.3 ng prolactin with 25 mg, iv; P less than .05). Similarly, sulpiride, a D-2 dopamine receptor blocker, induced an increase in serum prolactin, which appeared to be maximal at a dose of 25 mg (6,556.3 +/- 636.9 ng prolactin/420 min compared with 6,594.5 +/- 169.3 ng prolactin/420 min with 100 mg sulpiride; P less than .10). Finally, bromocriptine, a dopamine agonist, decreased serum prolactin compared with vehicle-injected controls, but the inhibitory effect was found only when basal levels of serum prolactin were highest (in May). These data suggest that mechanisms controlling prolactin secretion in the mare are similar to those described in other mammalian species, and that the seasonal decline in serum prolactin is not the result of increased sensitivity to the proposed prolactin-inhibiting factor, dopamine.

Animals↗

Seasonal and photoperiod-induced changes in serum prolactin and pituitary responsiveness to thyrotropin-releasing hormone in the mare.

Experiments were conducted in the horse mare to study the effects of photoperiod and season on serum prolactin and pituitary responsiveness to thyrotropin-releasing hormone (TRH). Increasing the photoperiod to 16 hr light:8 hr dark beginning in December (Experiment 1) and September (Experiment 2) increased serum prolactin, but the rate of increase was greater when the photoperiod treatment was initiated in September. In addition, TRH-induced prolactin secretion was found to be affected by season, in that pituitary secretion (net increase in prolactin and total prolactin secreted) was significantly greater in June compared with that of January (Experiment 3). These data suggest that in the mare, photoperiod plays an important role in controlling circulating levels of prolactin, but that in addition to photoperiod, other seasonally related factors, such as temperature, are involved in modulating the seasonal rhythm of serum prolactin.

Animals↗

Luteinizing hormone secretion from anterior pituitary cells of the cockerel: evidence for an ultradian rhythm.

Studies were conducted to characterize the secretory pattern of luteinizing hormone (LH) from perfused anterior pituitary cells of the cockerel in the presence and absence of secretagogues. Basal LH secretion was found to occur in a rhythmic pattern, with the mean cycle period for 5 different perfusion columns estimated to be 66.4 +/- 4.0 min. By contrast, when cells were repeatedly exposed to luteinizing hormone-releasing hormone (LHRH) at 90-min intervals, the period of the LH rhythm was altered to approximate the interval of LHRH pulses (96.7 +/- 6.1 min; n = 3 perfusion columns). Exposure of cells to media containing 50 mM potassium chloride (KCl) augmented the release of LH and slightly decreased the cycle period compared to that which occurs during basal secretion (49.2 min) but did not eliminate the rhythm. Finally, perifusion of cells with medium containing 10 microM colchicine eliminated the rhythm of secretion. These data suggest that there exists an ultradian rhythm of LH secretion from the chicken pituitary which is expressed in the absence of hypothalamic input and is modified by the hypothalamic releasing factor, LHRH. In addition, the rhythm does not seem to be affected in the short-term by a small depolarization of the membrane as occurs with the addition of KCl to the perifusion media but does seem to be dependent upon microtubule function.

Activity Cycles↗

Affinity chromatography of the anterior pituitary D2-dopamine receptor.

The D2-dopamine receptor from bovine anterior pituitary has been solubilized with digitonin and purified approximately 1000-fold by affinity chromatography on a new affinity support. This support consists of a (carboxymethylene)oximino derivative of the D2-selective antagonist spiperone (CMOS) covalently attached to Sepharose 4B through a long side chain. The interaction of the solubilized receptor activity with the affinity gel was biospecific. Dopaminergic drugs blocked adsorption of solubilized receptor activity to the CMOS-Sepharose with the appropriate D2-dopaminergic potency and stereoselectivity. For agonists, (-)-N-n-propylnorapomorphine greater than 2-amino-6,7-dihydroxytetrahydronaphthalene approximately equal to apomorphine greater than dopamine, whereas for antagonists (+)-butaclamol much greater than (-)-butaclamol. The same D2-dopaminergic specificity was observed for elution of receptor activity from the gel. To observe eluted receptor binding activity, reconstitution of the eluted material into phospholipid vesicles was necessary. Typically, 70-80% of the solubilized receptor was adsorbed by CMOS-Sepharose, and 40-50% of the adsorbed activity could be recovered after reconstitution of the eluted material. The overall recovery of D2-receptor activity from bovine anterior pituitary membranes was 12-15% with specific binding activity of approximately 150 pmol/mg. The reconstituted affinity-purified receptor bound ligands with the expected D2-dopaminergic specificity, stereoselectivity, and rank order of potency.

Animals↗

Distal tibial fractures in dogs and cats.

A total of 43 fractures of the distal tibia in dogs and cats were evaluated for fracture patterns, methods of stabilization, and time to bone union. Fractures of the metaphysis (9.3%), physis (30.9%), epiphysis (2.3%), and malleoli (58.2%) were classified. Open reduction and internal fixation, with combinations of Kirschner wire, orthopedic wire, and bone screws, were the methods of fixation used in the majority of fractures. These relatively simple methods of fixation were applied to all sizes of dogs and cats and resulted in an average bone healing time of 6 weeks.

Animals↗

Fractures of the tibial diaphysis in dogs and cats.

One hundred ninety-five fractures of the canine and feline tibial diaphysis were reviewed. Signalment of the animal; cause, location, and description of the fracture; treatment of the fracture, and response of the fracture to treatment were evaluated. Spiral and oblique fracture patterns were the most frequent in both juvenile (animals less than 12 months old) and adult animals (animals more than 12 months old). Comminuted fractures and open fractures were seen more commonly in the adult animal. Closed reduction and external coaptation as a method of repair was used more frequently in juveniles and open reduction and internal fixation was used more frequently in adults. When open reduction and internal fixation was used, pins, wires, and Kirschner Ehmer external splints were used more frequently in juveniles, and plate and screw fixation of the fracture was used more frequently in adults. The time to bone union varied with age of the animal and method of fixation. Healing times increased in adults, and increased as the stability of the fracture fixation increased. Complications included osteomyelitis and nonunions. Nonunions developed in 4.1% of the fractures not lost to follow-up.

Animals↗

Induction of yeast DNA ligase genes in exponential and stationary phase cultures in response to DNA damaging agents.

UV-irradiation of stationary phase cells of Saccharomyces cerevisiae and Schizosaccharomyces pombe leads to a 9-fold and 90-fold increase in transcript levels from the respective DNA ligase genes CDC9 and CDC17, whereas exponential cells show only 3-fold and 2-fold increases. Induction of CDC9 after MMS treatment and gamma-irradiation was also observed by using a CDC9-lacZ translational fusion and assaying for beta-galactosidase. Surprisingly, irradiation of S. cerevisiae induces only a 50% increase in DNA ligase itself, probably reflecting the extremely high in vivo stability of the enzyme. The UV-induction of ligase may be part of a "fail-safe" mechanism which, together with the enzyme stability, ensures adequate supplies of this essential enzyme.

DNA Damage↗

The expression in meiosis of genes which are transcribed periodically in the mitotic cell cycle of budding yeast.

The mitotic cell cycle genes CDC 8, 9 and 21 in Saccharomyces cerevisiae, together with the histone H2A gene, are transcribed discontinuously in meiosis. Message from all four genes initially declines in amount, then increases abruptly to reach maximal levels during premeiotic DNA synthesis before again declining. This response occurs only in meiotic cells; in asporogenous diploids the transcript simply declines in amount. In contrast, message from four genes with no known specific meiotic function (including the actin gene) shows the same profile in both sporogenous and asporogenous diploids. In mitotic cells the three CDC genes appear to be transcribed at the same time in the cell cycle, whereas in meiosis their transcripts accumulate with different kinetics, suggesting either that they have different turnover rates in meiotic cells or that the timing of their transcription is different.

Actins↗

Breeding experience modulating androgen dependent courtship behavior in male ring doves (Streptopelia risoria).

Courtship behavior of reproductively experienced males was compared with that of age-matched inexperienced males before and after castration and during treatments with hormones (testosterone propionate and estradiol benzoate). Inexperienced males displayed significantly lower levels of nest-oriented courtship, the nest-cooing (nest-soliciting) and wingflippings; however, agonistic courtship, the bow-cooing, was not affected by breeding experience. The lower level of nest-cooing display in the inexperienced males persisted even when their circulating level of androgen as measured by RIA was no different from that of experienced males. Estrogen treatments, however, produced no group difference in levels of nest-coo display. These results were discussed in the context of hormone-behavior relationships.

Animals↗

Pulsatile administration of gonadotropin-releasing hormone advances ovulation in cycling mares.

Cycling standardbred mares were infused with saline or 20 micrograms gonadotropin-releasing hormone (GnRH) in a pulsatile pattern (one 5-sec pulse/h, 2 h or 4 h) beginning on Day 16 of the estrous cycle. Although serum concentrations of luteinizing hormone (LH) increased significantly earlier in all three GnRH-treated groups (within one day of the initiation of infusion) compared to saline-infused controls, there were no differences in peak periovulatory LH concentrations among treatments (overall mean +/- SEM, 8.98 +/- 0.55 ng/ml). The number of days from the start of treatment to ovulation was significantly less in mares infused with 20 micrograms GnRH/h (mean +/- SEM, 2.9 +/- 0.6 days after the initiation of treatment, or 18.9 days from the previous ovulation; N = 7) compared to mares treated with saline (5.9 +/- 0.3 days, or 21.9 days from previous ovulation; N = 7) or 20 micrograms GnRH per 4 h (5.4 +/- 0.9 days or 21.4 days from previous ovulation; N = 5). Although mares infused with 20 micrograms GnRH/2 h ovulated after 4.3 +/- 0.7 days of treatment (Day 20.3; N = 7), this was not significantly different from either the control or 20 micrograms GnRH/h treatment groups. Neither the duration of the resulting luteal phase nor the length of the estrous cycle was different between any of the treatment groups (combined means, 14.7 +/- 0.2 days and 21.3 +/- 0.4 days, respectively). We conclude that pulsatile infusion of GnRH is effective in advancing the time of ovulation in cycling mares, but that the frequency of pulse infusion is a critical variable.

Animals↗

Aetiology of urinary symptoms in sexually active women.

Two hundred and fifty six unselected women, 50 of whom had urinary symptoms (frequency of urination or dysuria, or both), and who were attending a department of genitourinary medicine, were investigated. The urinary symptoms were associated both with pyuria and the isolation of undoubted pathogens from midstream urine (MSU) specimens. No associations were found between urinary symptoms and the isolation of Neisseria gonorrhoeae or Chlamydia trachomatis from the urethra or cervix; the recovery of Mycoplasma hominis from the urethra, cervix, or MSU; the recovery of Trichomonas vaginalis or Candida albicans from the vagina; or the presence of bacterial vaginosis. Urethral leucocytosis was associated with the isolation of T vaginalis but not with the recovery of N gonorrhoeae, C trachomatis, C albicans, or urinary pathogens. Pyuria was associated with the isolation of urinary pathogens and with the presence of trichomoniasis; it was not associated with the recovery of C trachomatis or M hominis.

Adolescent↗

The Northwick Park Study of first episodes of schizophrenia. I. Presentation of the illness and problems relating to admission.

Patients referred over 28 months from nine medical centres for a trial of prophylactic neuroleptic medication following first episodes of schizophrenic illness (462) were assessed with the Present State Examination, WHO scales for disability, past history, and sociodemographic factors, and a rating of disturbed behaviour; 253 fulfilled the study criteria; of the 209 who did not, 54 did not meet the diagnostic criteria, 65 had a history of a previous episode, and in 15 the psychotic illness was found to have an organic basis. The interval between onset of illness and admission varied widely, but was often more than one year and associated with severe behavioural disturbance and family difficulty e.g. in arranging appropriate care. Current arrangements for initiating management of first schizophrenic illnesses are frequently unsatisfactory.

Adolescent↗

A randomised controlled trial of prophylactic neuroleptic treatment.

Out of 253 patients fulfilling criteria for a first episode of schizophrenic illness, 120 entered a randomised placebo-controlled trial of maintenance neuroleptic medication on discharge; they were followed to relapse or loss to follow-up, for two years or to the end of the study. Of those on active medication, 46% relapsed, as did 62% of those on placebo; the most important determinant of relapse was duration of illness prior to starting neuroleptic medication. This finding might be because extended duration of symptoms before admission is more likely to be present in illnesses which in any case will have poor prognosis, or because susceptibility to relapse is reduced by early institution of treatment. The study provides no data on which a decision between these alternative explanations can be based.

Adolescent↗

Short-term outcome in trial entrants and trial eligible patients.

Of 253 patients from nine medical centres identified with first episodes of schizophrenic illness, 17 did not achieve discharge during the period of trial recruitment. 120 entered a randomised controlled trial of neuroleptic medication and were followed-up, as were 116 who were eligible for the trial but did not enter it. Overall, 60% of the sample had relapsed within two years of discharge; age, sex, ethnic origin, duration of admission, social withdrawal before admission, and type of onset of illness were not significantly related to relapse. Relapse rates were lower on active trial or standard medication than placebo, but however assessed, outcome at this early stage was poor for many patients.

Adolescent↗

Expressed emotion and relapse.

The relatives of 82 patients in a study of first episodes of schizophrenia were interviewed within six weeks of the index admission; 77 patients were subsequently discharged, and were followed to relapse or readmission. Analysis of relapse-free survival time was used to examine whether the components of 'expressed emotion' predicted relapse or response to neuroleptic medication: 'critical comments' by relatives was the only component present often enough to be used and was inversely related to 'social contact'. When preadmission duration of illness, and neuroleptic medication following discharge (identified previously as significant predictors of outcome) were taken into account, neither 'critical comments' nor 'social contact' were related to outcome nor to response to medication. The constellation of factors suggested as pathogenic was present only in a minority of cases: many patients lived alone and of those that were with families, most were not in high face-to-face contact with other members. The failure of the components of 'expressed emotion' to predict outcome or response to neuroleptic medication suggests that at best, such factors are weak predictors of liability to relapse. Their influence is unlikely to be comparable in magnitude to that of neuroleptic medication.

Adolescent↗

Serum concentrations of prolactin, thyroxine and triiodothyronine relative to season and the estrous cycle in the mare.

Studies were conducted to characterize circulating concentrations of prolactin, thyroxine (T4) and triiodothyronine (T3) relative to season and the estrous cycle, and to evaluate the ability of thyrotropin-releasing hormone (TRH) to induce prolactin secretion in the horse mare. The increase in serum prolactin following the iv injection of 0, 5, 50 and 500 micrograms TRH was dose-related, while all three doses of TRH induced a significant and comparable increase in serum T4. Seasonal variations in serum prolactin were directly correlated (P less than .001) with changes in photoperiod (r = .80) and temperature (r = .61). By comparison, concentrations of T3 were inversely related to temperature (r = -.49; P less than .001), while changes in T4 were less closely associated with photoperiod (r = -.29; P = .04). There were no significant fluctuations in prolactin, T3 or T4 at any stage of the estrous cycle. These results demonstrate that concentrations of prolactin in the mare are highest during the summer and lowest during the winter, but it is unknown whether this annual rhythm is controlled by photoperiod, temperature and(or) other environmental factors.

Animals↗