This review describes how the classic gut hormone, cholecystokinin (CCK), should be comprehended in 2025. In the early physiological tradition of studying gastrointestinal hormones, the hormones were named after the function that lead to their discovery. Hence, in 1928, the hormonal factor in the upper gut that regulated gallbladder contraction was called cholecystokinin. In 1968, Viktor Mutt and Erik Jorpes identified the porcine structure of this factor as an O-sulfated and carboxyamidated peptide of 33 amino acid residues (CCK-33). Its C-terminal bioactive heptapeptide amide turned out to be homologous to that of the antral hormone, gastrin. The structure allowed in vitro synthesis of peptide fragments for physiological studies and for production of CCK-antibodies for immunoassays and immunohistochemistry. Today, these tools have revealed CCK to be highly complex: CCK is a heterogenous, multifunctional peptide messenger system, widely expressed both in and outside the gut. Thus, the CCK gene encodes six different bioactive peptides (CCK-83, -58, -33, -22, -8, and -5) that are expressed in a cell-specific manner in O-sulfated and non-sulfated forms. Moreover, CCK peptides are not only hormones. They are also potent neurotransmitters, paracrine growth and satiety factors, anti-inflammatory cytokines, incretins, potential fertility factors and useful tumor-markers. Moreover, CCK has a phylogenetic history of nearly 600 million years. Particular interest has been given to the neuroscience of CCK, because CCK is the predominant peptide transmitter in the brain, expressed in amounts that surpass any other neuropeptide. Vice versa, the brain is the main production site of CCK in mammals.

Transient polyuria during pregnancy is reportedly caused by increased arginine vasopressin (AVP) degradation due to vasopressinase produced by the placenta. The mechanism underlying transient polyuria during pregnancy has not been established. In this study we measured urine volume, urine osmolality, and AVP transcriptional activity during pregnancy in wild-type and familial neurohypophysial diabetes insipidus (FNDI) mice. The FNDI mice were used as a partial AVP deficiency model. Vasopressinase was shown to be present in the placentas of pregnant mice. The Avp hnRNA level in the supraoptic nucleus, which is indicative of AVP transcriptional activity, was upregulated in wild-type and FNDI mice during late pregnancy. FNDI mice, but not wild-type mice, had a significant increase in urine volume and a decrease in urine osmolality during pregnancy. These data suggest that an increase in urine volume during pregnancy only occurs when the compensatory increase in AVP release is insufficient to counteract degradation by vasopressinase.