Parathyroid hormone‐related protein and mammary blood flow in the sheep

Abstract

SUMMARYClose-arterial infusion of fragment 1-34 of parathyroid hormone-related protein, at dose rates from 1 to 4 /ug/min for 20 min, increased mammary blood plasma flow in anaesthetized, nonlactating, parous sheep.

Increased mammary blood flow in the lactating goat induced by parathyroid hormone‐related protein

“…The present study demonstrates a rapid increase in MBF in the gland of the lactating goat in response to intramammary infusion of human synthetic PTHrP( -34), confirming the observation of Thompson (1993) that blood flow to the gland increased in response to similar infusion in non-pregnant, non-lactating sheep. However, the onset of the increase in rate of blood flow observed in the present study was between 10-and 15-fold faster and it occurred at a rate of infusion at least 10-fold lower than that used by Thompson (1993). Considering the greater dilution of PTHrP due to higher blood flow in the lactating gland, it would seem that the gland of the lactating goat is considerably more sensitive to PTHrP than that of the non-pregnant, non-lactating sheep.…”

“…However, the onset of the increase in rate of blood flow observed in the present study was between 10-and 15-fold faster and it occurred at a rate of infusion at least 10-fold lower than that used by Thompson (1993). Considering the greater dilution of PTHrP due to higher blood flow in the lactating gland, it would seem that the gland of the lactating goat is considerably more sensitive to PTHrP than that of the non-pregnant, non-lactating sheep.…”

“…If one accepts that the lattel is repr-esentative of the concentrations to which the mammilary vasculature is exposed, then the doses of PTHrP infused during the present study must represent pharmacological levels. Thompson (1993) similar-ly reported that the dose of PTHrP needed to induce an increase in blood flow in non-pregnant, non-lactating sheep was considerably greater than the measured concentraition in mammiaill.ry venous blood. Thus, the present data and those of Thomlpson (1993) suggest that endogenous PTHrP may not be an important regulator-y component of blood flow in the mlammaiizary gland, although no definitive conclusion can be mlade until local…”

“…This suggestion is strengthened further by the observation that the rise in mammary blood flow at lactogenesis in goats is preceded by an increase in PTHrP output into the mammary vein (Ratcliffe, Thompson, Care & Peaker, 1992) and that close-arterial infusion of PTHrP(l-34)amide stimulated mammary blood flow in non-pregnant, non-lactating sheep (Thompson, 1993). Since the lactating mammary gland is critically dependent upon an adequate supply of nutrients and hormonal stimuli from blood to sustain optimal milk synthesis, the importance of factors regulating supply of blood to the mammary gland is obvious.…”

Diseases of the Endocrine System

“…Vitamin D then facilitates increased active calcium absorption in the intestine and reticulorumen, 151 as well as further increasing resorption in the kidney. 153 It also is produced by the mammary gland in response to prolactin, where it has a role in increasing mammary blood flow 154,155 and affects mineral secretion in milk. Normal reported vitamin D levels are 23.8 ± 5.7 ng/mL and 40.7 ± 9.1 ng/mL in goats and sheep, respectively.…”