Mycoplasmas and ovine keratoconjunctivitis

The clinical course of an outbreak of keratoconjunctivitis in housed lambs and their dams was followed. Signs were transient generally and became severe in only a small proportion of lambs. The outbreak became most obvious when the lambs were 46 to 55 days old, when 46.9 per cent were affected. Mycoplasma conjunctivae isolations, confirmed by comparison with the type strain by biochemical and serological reactions, increased to 62.1 per cent of all eyes swabbed, but no correlation could be demonstrated between presence of the organism and clinical status. The reasons for this are discussed. Mycoplasma ovipneumoniae was also recovered from the eyes of a small number of lambs. Instillation of a broth culture of M conjunctivae into the conjunctival sacs of four hoggs produced a transient keratoconjunctivitis similar to that observed in the field, but no effect was observed in animals inoculated intravenously. M conjunctivae may therefore be the aetiological agent of non-follicular infectious ovine keratoconjunctivitis, although further work in gnotobiotic or specific pathogen free lambs is required to establish the fact beyond doubt.     

Interspersion of different repeated sequences in the wheat genome revealed by interspecies DNA/DNA hybridisation

The repeated sequences in oats DNA have been used to study chromosomal repeated sequence organisation in wheat. Approximately 75% of the wheat genome consists of repeated sequences but only approximately 20% will form heteroduplexes with repeated sequences from oats DNA at 60 degrees C in 0.18 M Na+. The proportion of wheat DNA that forms heteroduplexes with oats DNA is shown to be independent of the wheat DNA fragment length. However, the proportion of wheat DNA that is retained with the heteroduplexes when fractionated on hydroxyapatite is very dependent upon the wheat fragment length up to 3500 nucleotides. This is because more non-renatured wheat DNA is attached to the heteroduplexes with longer fragments. The results indicate that the repeated sequences in the wheat genome homologous to repeated sequences in oats are not clustered in the chromosomes but distributed amongst other repeated and possible non-repeated sequences.     

In vitro synthesis of beta1C/beta1A globulin (the C3 component of complement) by tissues and leucocytes of mice

The synthesis of beta1C/beta1A globulin (the C3 component of complement) was studied in in vitro cultures of mouse tissues and leucocytes. Often culture in medium containing 14C-labelled amino acids, the newly synthesized radioactively-labelled protein was identified by radioimmunoelectrophoresis. Synthesis was found in spleen, liver, trachea, lung and Peyer's patch tissue, but was only occasionally detectable in cultures of intestine. Cultures of the glass-adherent cells from bone marrow, blood, lung washings and subcutaneous tissue all showed strong synthesis, indicating that the ability to synthesize beta1C/beta1A is a property shared by mononuclear phagocytes from many sites. In contrast, the nonglass adherent cells showed no synthesis of beta1C/beta1A, although these cells were shown to be viable by their ability to synthesize immunoglobulins.     

Treatment of relapsing polychondritis with dapsone

Three patients with relapsing polychondritis were treated successfully with dapsone. Mounting evidence suggests an immune-related pathogenesis for relapsing polychondritis. Dapsone may be effective in certain immune-related diseases because of its inhibition of lysosomal enzymes.     

Propranolol in hypertension: a dose-response study

The effect of propranolol was studied in a double-blind crossover trial in 24 carefully selected hypertensive outpatients. Each patient received propranolol 60 mg/day, 120 mg/day, 240 mg/day, and placebo for four weeks each according to a randomised sequence. Propranolol 60 mg/day was no better than placebo in reducing blood pressure. The effects of propranolol 120 mg/day and 240 mg/day were not significantly different. Both doses reduced lying blood pressure by about 20/10 mm Hg from an initial level of 173/104 mm Hg. No difference was detected between the effects of the different doses of propranolol and placebo on weight or on the occurrence of adverse reactions.     

Thymic muscle cells bear acetylcholine receptors: possible relation to myasthenia gravis

Culture of dissociated thymus from rats and humans yielded cells identical to skeletal muscle with respect to morphology, contractility, electrophysiological properties, and the presence of acetylcholine receptors. These cells, strategically located in the thymus, may play a role in initiation of the autoimmune response against acetylcholine receptors, which is characteristic of myasthenia gravis.     

Combinations of hyperthermia (40 degrees, 45 degrees C) with radiation

Incubation of Chinese hamster cells at an elevated but sublethal temperature between fractions of radiation and/or pulses of hyperthermia at 45 degrees C strongly modified the effectiveness of cell killing. Increasing the incubation temperature from 37 to 40 degrees C between fractions of hyperthermia at 45 degrees C followed by radiation substantially enhanced cell killing; while the opposite sequence (radiation leads to incubation at 40 degrees C leads to hyperthermia at 45 degrees C) resulted in less effective cell killing than would have been expected from the independent interaction of hyperthermia and radiation alone. This suggests the use of short pulses of localized hyperthermia in the presence of physiologically tolerable fever followed by irradiation as one approach to the utilization of hyperthermia in cancer therapy.     

Renin and aldosterone suppression in the antihypertensive action of clonidine

In 18 hypertensive patients receiving a constant (100 mEq/day) sodium diet, treatment with clonidine (0.3 mg/day for 5 days) decreased blood pressure in 11 patients with high and normal renin levels and 7 with low renin levels. The high and normal renin group had early and rapid reductions in blood pressure and plasma renin activity. In contrast, the low renin group had a more gradual hypotensive response and only a small absolute decrease in plasma renin. For all patients, pretreatment renin levels were related to the initial decrease in blood pressure but not to the reductions measured after 5 days. Thus, two mechanisms of action of clonidine are possible, one related to acute inhibition of the renin-angiotensin system in patients with high and normal renin levels and another that is independent of renin mechanisms and occurs in all hypertensive patients. In six additional patients with high renin levels induced by prior sodium depletion (10 mEq/day sodium diet), clonidine did not reduce blood pressure or renin, thus indicating that the suppressive action of this agent on renin pressor mechanisms occurs only in patients whose elevated renin levels are intrinsic to hypertension and unrelated to sodium depletion. Of the 18 patients receiving a normal sodium diet, 13 were classified as responding to treatment (decrease in both systolic and diastolic pressures of at least 10%). The five nonresponders had greater weight gain and higher values for aldosterone excretion. For all patients, there was a significant correlation between decrements in blood pressure and in aldosterone, suggesting that the countervailing effects of fluid accumulation on blood pressure in nonresponding patients resulted from a failure of aldosterone to be suppressed. Changes in aldosterone, in turn, correlated significantly with changes in renin. Thus, the antirenin effect of clonidine enhances its antihypertensive action not only by acutely ablating renin-angiotensin pressor mechanisms, but also by inhibiting aldosterone production and thereby minimizing longer-term reactive volume retention during treatment.