High-contrast terawatt chirped-pulse-amplification laser that uses a 1-ps Nd:glass oscillator.

We have developed a fiberless 1-TW all-Nd:glass chirped-pulse-amplification laser system that uses high-contrast 0.8-1.4-ps pulses produced directly from a Nd:glass feedback-controlled oscillator. Employing grating-only expansion and compression, the system produces clean (~10(7) contrast ratio) 1-J, 1- 1.4-ps recompressed pulses without added pulse cleaning. Clean microjoule-energy pulses from the oscillator require less subsequent amplification than cw oscillator schemes, thereby minimizing gain-bandwidth narrowing and offering improved contrast with amplified stimulated emission background.

Plasma antidiurectic hormone during hypoxia and anaesthesia in pigs.

The level of antidiuretic hormone (ADH) in the plasma of pigs was studied during hypozia, anaesthesia and a combination of the two conditions. Hypoxia, caused by making conscious pigs breathe nitrogen, elicited a rise in the level of ADH without change in plasma osmolality; the hypoxia was accompanied in some cases by a slight lowering of arterial pressure which quickly returned to its original level after the period of hypoxic breathing. Pentobarbitone anaesthesia had no significant effect on the level of ADH but halothane anaesthesia elicited a rise in ADH. Transient high levels of ADH were seen in animals which were exposed to hypoxia during halothane or pentobarbitone anaesthesia. These high levels of ADH were sometimes, but not invariably, accompanied by a fall in arterial pressure. No consistent changes in plasma osmolality or haematocrit were associated with the raised plasma ADH.

Effect of environmental temperature and food intake on the distribution of fat in growing hairless mice.

1. The fat content of the skin and of the skin-free carcass was measured in young, growing hairless mice about 4-8 weeks old kept at either 22 degrees (cool environment, i.e. below their critical temperature) or at 33 degrees (warm environment; i.e. within their thermoneutral range). The food intake of groups of the mice reared at each temperature was restricted to between 77 and 89% of that of a litter-mate fed ab lib. 2. In all the mice, whether fed ad lib. or on a restricted intake, those reared in the warm environment contained about 1-5 times as much fat as those reared in the cool environment. At both temperatures and feeding levels, approximately 25% of the total body fat was present in the skin. 3. Each mouse reared at 33 degrees on an ad lib. regimen reached about the same plateau weight in the same period as its litter-mate reared at 22 degrees. However its food intake during this period of growth was only about half that of the mouse reared at the lower temperature, so its food conversion ratio (dry food intake:body-weight gain) was twice as efficient. 4. It is concluded that neither the growth rate nor the distribution of fat within the body of the growing mouse can be influenced by rearing the animals at these different environmental temperatures. Rearing at the higher temperature, however, both decreases food intake and also promotes deposition of more fat within the body.

The effect of hormones and of an osmotic gradient on the structure and properties of mammalian foetal urinary bladder in vitro.

1. Water and isotope fluxes were measured by incubating urinary bladders of foetal pigs and sheep in vitro in the presence and absence of a concentration and osmotic gradient. The structure of the urinary bladder of foetal pigs under various conditions was studied by electron microscopy. Its ultrastructure was found to be closely similar to that of foetal sheep. 2. Antidiuretic hormone (ADH) (0-2 U. ml-1) enhanced the enlargement of intercellular spaces caused by dilute mucosal medium in pig bladders; prolactin (1 u. ml-1) prevented osmotic dilatation of the intercellular spaces. 3. The hydraulic conductivity, Lp, was estimated to be 0-5 X 10 (-7) cm.s-1atm-1 in sheep and pigs at about 100 days gestation; the ratio of osomotic to diffusional permeability, (LpRT/VW)/PD, in the presence and absence of ADH, was 2-1 and 1-6 respectively. These are similar to the values found in fish gills. 4. Prolactin reduced bulk flow of water to zero in seven out of eight bladders investigated. Incubation with ADH or vasotocin (55 mu. ml-1) in the presence of prolactin restored water flux to 22% and 45% of control values respectively. 5. There was no significant net flux of sodium from mucosa to serosa in pig bladder except in the presence of prolactin. No net flux of sodium occurred from mucosal to serosal side of pig or sheep bladders in the presence of an adverse electrochemical gradient, although in sheep the permeability ratio was significantly greater than one. 6. The diffusional flux ratio for water remained unity under all conditions; vasotocin increased unidirectional fluxes and prolactin reduced them. The flux ratios were unaffected by the direction of bulk fluid flow, probably because diffusion was rapid compared to flow: the ratio of diffusional flux to volume flow was between 11 and 18.

Effects of various ambient temperatures and of heating and cooling the hypothalamus and cervical spinal cord on antidiuretic hormone secretion and urinary osmolality in pigs.

1. Plasma ADH concentration, urinary and plasma osmolality and haematocrit were measured in young pigs placed in cold, thermoneutral, warm and hot ambient temperatures. In some experiments a thermode placed in the hypothalamus or over the cervical spinal cord was heated or cooled at various ambient temperatures. 2. Plasma ADH concentration remained at a low level (0-5--5 muu. ml.-1) over 2 hr or 3 hr periods when the pigs were in cold, thermoneutral or warm ambient temperatures. A hot environment, which caused a marked rise in the pigs' rectal temperature, was associated with a large rise in plasma ADH level. 3. The rise in plasma ADH level which occurred during an increase in body temperature was consistently and completely suppressed by simultaneous cooling of the thermode in the pre-optic region to 5 to 10 degrees C. When the thermode was in the region of the supraoptic nucleus the rise in ADH was only partly suppressed, and when it was over the cervical cord it was only sometimes suppressed. 4. Cooling the thermodes in any position at a cold or thermoneutral ambient temperature, or heating them at a thermoneutral or warm ambient temperature, caused no consistent change in ADH. 5. A diuresis, with a urinary flow-rate of at most 1 ml. min-1 and minimal urinary osmolality of 53 m-osmole kg-1, was observed on only three occasions, twice during cooling of a thermode in the hypothalamus and once after the end of a period when the thermode was heated. In each case, the plasma ADH was less than 2 muu. ml.-1. 6. A slight rise of haematocrit in cold ambient conditions and a slight fall in the warm were observed. Otherwise changes in haematocrit were trivial, and a shift of water between vascular system and interstitium could not be invoked to account for changes in ADH levels. Observed variation of plasma osmolality was also slight.

Structure and function in urinary bladder of foetal sheep.

1. The structure and function of the epithelial lining of the urinary bladder of sheep foetuses was investigated by electron microscopic studies made in conjunction with a series of experiments in which the permeability of the bladder to sodium and water was measured in vitro. Measurements were made at gestational ages ranging from 50 to 141 days (term = 147 days) Osmolarity and electrolyte concentrations of urine found in the foetal bladder were also measured.2. The development of tight junctions between the bladder epithelial cells was investigated by incubating the tissue with solutions containing 1 mM-LaCl(3) on the mucosal surface. No penetration of the junctions by lanthanum was observed in foetuses of 90 days or older. In younger bladders, the epithelial layer was stripped by treatment with lanthanum, but tight junctions appeared to be fully developed in early bladders incubated without lanthanum.3. The surface structure of the luminal (mucosal) plasmalemma was fully developed at 50 days.4. Unidirectional fluxes of labelled sodium and water were measured with identical solutions bathing the two surfaces of the bladder wall. No net water movement occurred; the mean ratio of efflux to influx in nine bladders was 1.002 +/- 0.039 (S.E. of mean). Under these conditions, the flux ratio for sodium was 1.735 +/- 0.143 (S.E. of mean) in twelve bladders.5. Antidiuretic hormone (ADH) had no effect on net water movement but reduced the net efflux of sodium so that the flux ratio became 1.285 +/- 0.255 (S.E. of mean) n = 8. ADH also had a striking effect on the structure of the epithelium, causing marked swelling of the intercellular spaces. The tight junctions remained an effective barrier to lanthanum penetration under these conditions; lanthanum was not observed in the enlarged spaces.

The effect of urea loading on volume and concentration of urine in rabbits.

1. To find how urea contributes to the water-conserving ability of a herbivore's kidney, groups of ten young rabbits on a low-protein diet and at three different levels of dietary electrolyte were given 1.8 g urea by mouth daily for 3 days. Vasopressin was administered daily to half the animals in each group.2. The urinary osmolarity and urea output of each animal was recorded daily during the urea loading and for a 3-day control period before and after loading. The renal water requirement for non-urea solute output (defined as daily volume/daily non-urea solute output) was calculated. The sodium content of renal cortex and medulla was measured in some animals from each group.3. Urea caused additional water excretion only in those rabbits which were receiving the low-salt diet. There was invariably increased water excretion when the ratio of urea to non-urea solute output exceeded 2.4. In most of the rabbits on normal-salt and high-salt intake, urea produced little change in the volume in which non-urea solute was excreted. Three out of the ten high-salt animals showed significant reduction of this volume during urea-loading.5. Vasopressin significantly reduced the volume required for non-urea solute output, but the effect of vasopressin was independent of urea-loading and of dietary electrolyte level.6. The low-electrolyte diet significantly reduced the sodium concentration in the rabbits' renal medullary tissue.7. It is concluded that in rabbits urea contributes to water retention mainly by its high permeability, enhanced by vasopressin, which permits maximal water reabsorption in the renal medulla. Water retention by means of uphill transport of urea, if it occurs at all, is slight.

Kidney composition and renal concentration ability in young rabbits.

1. The water, sodium, urea, potassium and ammonia concentrations of the kidney cortex and inner medulla of adult rabbits, and of rabbits 1, 4, 14 and 21 days old, were measured after mild dehydration. The urine osmolarity and serum and urine urea concentrations were also measured.2. Potassium and ammonia showed no consistent variation in the different parts of the kidney or at the different ages. Sodium concentrations expressed as m-equiv/100 g fresh weight were about twice as high in the medulla as in the cortex at all ages.3. The medulla/cortex ratio of urea concentration increased markedly between the fourteenth and twenty-first day after birth. So also did the urine osmolarity of the mildly dehydrated animals.4. The rise in the medulla/cortex urea ratio between birth and 21 days, and the even higher ratio found in adult animals, was due to a decrease in the concentration of urea in the cortex rather than to an increase in its concentration in the medulla.