The large variability in kidney morphology among fish makes it difficult to build a “universal” model on its function and structure. Therefore, a morphological study of brown trout trunk kidney was performed, considering potential seasonal and sex effects. Three-year-old specimens of both sexes were collected at four stages of their reproductive cycle. Kidney was processed for light and electron microscopy. The relative volumes of renal components, such as renal corpuscles and different nephron tubules, were estimated by stereological methods. Qualitatively, the general nephron structure of brown trout was similar to that described for other glomerular teleost species. Quantitatively, however, differences in the relative volume of some renal components were detected between sexes and among seasons. Particularly, highest values of vacuolized tubules and new growing tubules were observed after spawning, being more relevant in females. Despite seasonal changes, more linear correlations were found between those parameters and the reno-somatic index than the gonado-somatic index. Thus, we verified that some brown trout renal components undergo sex dependent seasonal variations, suggesting a morphological adaptation of the components to accomplish physiological needs. These findings constitute a baseline for launching studies to know which factors govern the morphological variations and their functional consequences.

The prenatal diet can program an individual's cardiovascular system towards later higher resting blood pressure and kidney dysfunction, but the extent to which these programmed responses are directly determined by the timing of maternal nutritional manipulation is unknown. In the present study we examined whether maternal nutrient restriction targeted over the period of maximal placental growth, i.e. days 28–80 of gestation, resulted in altered blood pressure or kidney development in the juvenile offspring. This was undertaken in 6-month-old sheep born to mothers fed control (100–150 % of the recommended metabolisable energy (ME) intake for that stage of gestation) or nutrient-restricted (NR; 50 % ME; n 6) diets between days 28 and 80 of gestation. Controls were additionally grouped according to normal (>3, n 7) or low body condition score (LBCS; <2, n 6), thereby enabling us to examine the effect of maternal body composition on later cardiovascular function. From day 80 to term (approximately 147 d) all sheep were fed to 100 % ME. Offspring were weaned at 12 weeks and pasture-reared until 6 months of age when cardiovascular function was determined. Both LBCS and NR sheep tended to have lower resting systolic (control, 85 (SE 2); LBCS, 77 (SE 3); NR, 77 (SE 3) mmHg) and diastolic blood pressure relative to controls. Total nephron count was markedly lower in both LBCS and NR relative to controls (LBCS, 59 (SE 6); NR, 56 (SE 12) %). Our data suggest that maternal body composition around conception is as important as the level of nutrient intake during early pregnancy in programming later cardiovascular health.

The kidneys of Anna's hummingbird (Calypte anna) differ in several significant ways from those of other birds that have been examined. The kidneys of this nectarivore contain very little medullary tissue; 90% of the total volume of the kidneys is cortical tissue, with medulla accounting for only an additional 2%. More than 99% of the nephrons are the so-called ‘reptilian type’), which lack the loop of Henle. The few looped (‘mammalian type’) nephrons are incorporated into only a few medullary cones per kidney. The loopless nephrons are similar to those of other birds. However, the looped nephrons differ in that they lack the thin descending limb of the loop of Henle, which is found in other birds and is thought to play an important role in the countercurrent multiplier system in the avian kidney. Instead, the cells of the nephron segment following the pars recta of the proximal tubule resemble those of the thick ascending limb, with the large populations of mitochondria that are typical of transporting epithelia and no reduction in cell height. The absence of a descending thin limb in Anna's hummingbird is not necessarily a correlate of the hummingbird's liquid diet, because thin limbs have been documented in the kidneys of two other hummingbird species, the rufous hummingbird (Selasphorus rufus) and the broad-tailed hummingbird (Selasphorus platycercus). The functional correlates of the unique renal morphology in Anna's hummingbird warrant further study.