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<span>Previous trials have demonstrated that sheep on a low protein diet and free access to water, and sheep dosed with boluses of NaCl intraruminally also with free access to water, showed decreases in urea loss via the urine compared to control animals. <br />We monitored urea excretion in sheep on a relatively poor protein diet when they were exposed to saline drinking water, i.e. they were unable to vary their intake of NaCl:water. <br />Sheep on isotonic saline drinking water (phase 3) excreted significantly more urea via the urine (284 mM/day) compared to phase 1 when they were on non-saline drinking water (urea excretion = 230 mM/day) and phase 2 when they were on half isotonic saline drinking water (urea excretion = 244 mM/day).This finding was explained by the high glomerular filtration rate (GFR) 91.9 <em>ℓ</em>/day, compared to 82.4 <em>ℓ</em>/day (phase 1) and 77.9 <em>ℓ</em>/day (phase 2), together with a significantly raised fractional excretion of urea (FE_urea) (51.1 %) during this phase, and was in spite of the significantly lower plasma concentrations of urea in phase 3 compared to phase 1. The FE_urea probably results from the osmotic diuresis caused by the salt. There were indications of a raised plasma antidiuretic hormone (ADH) concentration and this would have opposed urea loss, as ADH promotes urea reabsorption. However, this ADH effect was probably counteracted to some extent by a low plasma angiotensin II concentration, for which again there were indications, inhibiting urea reabsorption during the phases of salt loading. <br />As atrial natriuretic peptide both increases GFR and decrease sodium reabsorption from the tubule, it was probably instrumental in causing the increase in GFR and the increase in the fractional excretion of sodium (FE_Na).</span>

Misinterpretation of why black students do not pursue studies in the biological sciencesWe contest the findings and methodology of the recently published commentary (Nattrass N., S Afr J Sci. 2020; 116(5/6), Art. #7864). We echo the many previous voices and calls for concern over the tenuous methodology and unsubstantiated 'conclusions' of this commentary. Below we provide specific details about each of the instances where this commentary is technically unsound. General premiseThe premise of the commentary is itself flawed. Biology students in other universities reflect the racial profile of the country. For instance, data from our own institution indicate that black student enrolment in the biological sciences has nearly doubled in the last decade (from ~640 students in 2010 to 1150 students in 2020), while other groups' enrolment has remained constant. Consequently, the assumption in the title: that black students are not choosing biological sciences is not valid.

The importance of angiotensin II in the regulation of water and electrolyte balance in sheep is questionable. In this trial the effects of an angiotensin-converting enzyme (ACE) inhibitor were quantified in sheep on restricted water intake. Comparing the phase of water restriction only with that of water restriction plus ACE inhibition, significant increases were observed during the latter phase in urine volume, sodium and potassium excretion <em>via</em> the urine, sodium concentration in the plasma and osmolar clearance. Urine osmolarity decreased with inhibition of angiotensin II formation while variables such as water, sodium and potassium loss <em>via</em> the faeces were unaffected. Most of the renal effects of ACE inhibition, except the increase in urinary potassium excretion, were explicable in terms of the established functions of angiotensin II. Furthermore, results of this trial indicate that angiotensin II has no significant effect on the intestine in regulating water and electrolyte excretion <em>via</em> the faeces